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J Barbosa

Publications and source records attributed to J Barbosa.

At least 19 recordsLinked to original sources
PubMed2006

Determination of a series of quinolones in pig plasma using solid-phase extraction and liquid chromatography coupled with mass spectrometric detection Application to pharmacokinetic studies.

A simple and sensitive liquid chromatography (LC) method was developed for the simultaneous determination of eight quinolones in pig plasma samples. The following two methods of detection were used: ultraviolet (UV) and mass spectrometry with electrospray ionization (ESI/MS). Sample preparation consisted of solid-phase extraction (SPE) on Strata X cartridges prior to the analysis by LC/UV or LC/ESI/MS. The recovery, linearity, limit of detection (LOD) and limit of quantification (LOQ), precision and accuracy of the method were evaluated using spiked pig plasma samples. The suitability of the method for pharmacokinetic studies was evaluated by determining the concentrations of enrofloxacin (ENR) and ciprofloxacin (CIP) also in pig plasma, after administration of 200mg of enrofloxacin per kilogram of fodder during 5 consecutive days.

Animals↗
PubMed2006

Confirmatory and quantitative analysis using experimental design for the extraction and liquid chromatography-UV, liquid chromatography-mass spectrometry and liquid chromatography-mass spectrometry/mass spectrometry determination of quinolones in turkey muscle.

The aim of this work is to established methods for determination of quinolones (ciprofloxacin, danofloxacin, enrofloxacin, difloxacin and flumequine), regulated by European Union, and sarafloxacin in turkey muscle. An experimental design has been applied for the optimization of the factors that influence the extraction of quinolones from turkey muscle in order to determine the experimental conditions for their extraction with high recoveries. Liquid chromatography with ultraviolet detection (LC-UV), liquid chromatography-mass spectrometry (LC-MS) and liquid chromatography tandem mass spectrometry (LC-MS/MS) have been used for the simultaneous quantification of quinolones antibiotics in turkey muscle. The proposed methods have been validated according to the Food Drugs Administration guideline and presents the limit of quantification below the maximum residue limits established by the European Union for quinolones in turkey muscle. The methods developed have been applied to quantification of enrofloxacin and its main metabolite ciprofloxacin in samples of turkey muscle obtained from animals treated with enrofloxacin.

Animals↗
PubMed2005

Development of analytical methods for multiresidue determination of quinolones in pig muscle samples by liquid chromatography with ultraviolet detection, liquid chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry.

This paper presents a comparison between liquid chromatography with ultraviolet detection (LC-UV), liquid chromatography-mass spectrometry (LC-MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods developed for the multiresidue determination of 8 quinolones, around their maximum residue levels (MRLs) in pig muscle. The procedure involves common extraction of the quinolones from the tissues by traditional extraction, a step for clean-up and preconcentration of the analytes by solid-phase extraction (SPE) and a subsequent liquid chromatographic analysis. The methods present satisfactory results of linearity, precision and limits of quantification much lower than the MRLs established by the European Union for quinolones in pig tissues.

Animals↗
PubMed2004

Determination of quinolones in chicken tissues by liquid chromatography with ultraviolet absorbance detection.

This paper presents an analytical method for the determination of quinolones in chicken tissues. The procedure involves pre-treatment by solid-phase extraction (SPE) and subsequent liquid chromatography (LC) with UV absorbance detection. Different SPE disposable cartridges and extractants of the tissue samples were tested, and various columns were systematically tested. The mobile phase was composed of acetonitrile and citric buffer at pH 4.5, with an initial composition of acetonitrile-water (12:88, v/v) and using linear gradient elution. Recoveries were 66-91% in the concentration range 30-300 microg kg(-1). The detector response was linear in this range. The limits of detection were 16-30 microg kg(-1). These values were lower than the maximum residue limits established by the European Union.

Animals↗
PubMed2004

A follow up model for patients with atrophic chronic gastritis and intestinal metaplasia.

AIM: To devise a follow up model for patients with gastric cancer associated lesions, such as atrophic chronic gastritis (ACG) and intestinal metaplasia (IM). METHODS: Cohort study of 144 patients, followed for a minimum of one year, in whom at least two upper gastrointestinal endoscopic biopsies in flat gastric mucosa provided a diagnosis of ACG, IM, or low grade dysplasia (LGD). RESULTS: Of those diagnosed with ACG at first endoscopic biopsy (entry biopsy), 12% progressed to LGD in outcome biopsy, as did 8% of those with type I IM, 38% with type II or III IM, and 32% with LGD. Type of IM at entry independently predicted progression to LGD and cancer. Type II and III IM had a higher rate of progression to LGD than type I IM, which showed an indolent behaviour similar to ACG. Patients with type II or III IM were at higher risk for development of dysplasia, and 7% of patients with type III IM at first biopsy progressed to high grade dysplasia (HGD), whereas no cases of ACG or type I/II IM progressed to HGD during the first three years. CONCLUSION: Patients with ACG or IM could possibly be allocated to different management schedules, based on differences in rate and proportion of progression to LGD or HGD. Less intensive follow up (two/three yearly with "serological evaluation" (pepsinogen)) may suit those with ACG or type I IM. Patients with type III IM may benefit from six to 12 monthly improved endoscopic examination (magnification chromoendoscopy).

Adult↗
PubMed2003

Determination of fluoroquinolones in human urine by liquid chromatography coupled to pneumatically assisted electrospray ionization mass spectrometry.

The fluoroquinolones are synthetic antimicrobial agents widely used in human and veterinary medicine. The aim of this work was to develop a method of characterization and determination of three widely used fluoroquinolones (norfloxacin, ciprofloxacin and ofloxacin) in human urine by liquid chromatography (LC) coupled to pneumatically assisted electrospray ionization (ESI) mass spectrometry (MS). For this purpose, the operational parameters of the electrospray interface were optimized in order to obtain the best signal stability and the highest sensitivity of the fluoroquinolones. The three fluoroquinolones studied and enrofloxacin, used as internal standard, were extracted from human urine samples by solid-phase extraction (SPE) and the previously established LC-UV method was successfully coupled with the MS system. The mass spectra obtained provide adequate information for identification purposes. Quality parameters were determined and satisfactory results were obtained. Likewise, the method detection limit was about 10 ng ml(-1) for the three fluoroquinolones studied employing selected-ion monitoring mode.

Chromatography, Liquid↗
PubMed2003

Characterization of human transferrin glycoforms by capillary electrophoresis and electrospray ionization mass spectrometry.

Carbohydrate Deficient Glycoprotein Syndrome (CDGS) is an inherited metabolic disease affecting all parts of the body. The biochemical diagnosis of this syndrome is based on the presence of a special marker in blood, Carbohydrate Deficient Transferrin (CDT), which is also a marker of chronic alcohol abuse. CDT is characterized by abnormal glycoforms of serum transferrin (Tf). In the present study, electrophoretic separation of human serum transferrin glycoforms was carried out using a bare fused-silica capillary and the glycoforms present in commercial Tf were baseline separated. The limit of detection (LOD) of human Tf was around the nmol concentration range. The LOD of the trisialo- and disialo-Tf, expressed as percentages of the tetrasialo-Tf peak area, were 0.5% for trisialo-Tf and 0.4% for disialo-Tf, and these values were appropriate for CDGS diagnosis. Moreover, Tf glycoforms were characterized using mass spectrometry (MS). The method was applied to the analysis of normal and pathological serum samples, after dilution. The results obtained suggest a way of making a rapid and simple CDGS diagnosis.

Electrophoresis, Capillary↗
PubMed2003

Characterization of metallothionein isoforms from rabbit liver by liquid chromatography coupled to electrospray mass spectrometry.

Metallothioneins (MTs), a group of low molecular weight proteins found in practically all life forms, are characterized by high sulfur content and an affinity for metal ions. At acidic pH, MTs show metal depletion, leading to apothioneins. In the work described here, in order to optimize the separation of rabbit liver apothioneins using liquid chromatography (LC) with UV detection, the proportion of the organic modifier of the mobile phase was optimized by establishing relationships between Reichardt's E(N)(T) scale of solvent polarity and the chromatographic retention measured by the capacity factor, k. Additionally, such optimum separations were carried out in a LC-electrospray mass spectrometry (ES-MS) coupled system allowing the identification and characterization of the different rabbit liver apo-MT-forms. In this way, electrospray ionization mass spectrometry offers great possibilities aiming at a better understanding of metallothionein polymorphism.

Amino Acid Sequence↗
PubMed2003

Evaluation of chromatographic versus electrophoretic behaviour of a series of therapeutical peptide hormones.

In this work, models describing the effect of pH on chromatographic and electrophoretic behaviour for a series of polyprotic therapeutic peptide hormones were compared. taking into account the species in solution and the activity coefficients. The usefulness of the proposed equations is twofold, they permit the determination of the acidity constants in water and in the hydroorganic mobile phases used in liquid chromatography (LC) and capillary electrophoresis (CE) and can also be used for the selection of the optimum pH for the separation of mixtures of the modelled compounds. The proposed relationships allow an important reduction of the experimental data needed for the development of new separation methods. The accuracy of the proposed equations is verified by modelling the chromatographic and electrophoretic behaviour of a series of polyprotic therapeutic peptide hormones. By calculating the values of predicted resolutions, selection of the optimum pH to perform LC or CE separations of their mixtures becomes a rapid and simple process.

Chromatography, Liquid↗
PubMed2003

Use of Helicobacter pylori-specific antibodies in the evaluation of intestinal metaplasia and gastric dysplasia.

It is believed that Helicobacter pylori acts mainly during the initial phases of gastric carcinogenesis. Therefore, this study aims to assess the usefulness of H. pylori diagnosis in patients with chronic gastritis (CG), intestinal metaplasia (IM) and dysplasia--conditions that are associated with gastric cancer. A cross-sectional study of 94 patients was performed, which involved endoscopic biopsy and determination of specific serum anti-H. pylori antibodies (IgA, IgG and IgM) by enzyme-linked immunosorbent assay (ELISA). Biopsies were taken from the gastric antrum and corpus, and from endoscopic lesions. Two specimens per patient were used for bacterial culture. H. pylori infection status, used as the gold standard, was based on culture results. Validity measures were determined and receiver operating curve (ROC) was used to determine the best cut-off for serum antibody levels. Histopathological evaluation (n = 160) was performed independently by two pathologists. Lesions consistent with CG were found in 86 patients (91%), consistent with IM in 69 patients (73%) and with dysplasia in five patients (5%). In the 86 patients with CG, 38 (44%) were infected by H. pylori, as were 26 (38%) and one (20%) with IM and dysplasia, respectively (P=0.039). Area under the curve (AUC) was 0.40 (95% confidence interval [CI]: 0.28-0.51) for IgM, 0.69 (0.58-0.80) for IgA and 0.83 (0.74-0.92) for IgG for the diagnosis of H. pylori infection. Best cut-off was 41 u/mL for IgG, with a sensitivity (95% CI) of 90% (84-96%) and a negative predictive value (NPV) of 91% (85-97%). For IgA the results were 22 u/mL, 74% (65-83%) and 77% (68-86%), respectively. Prevalence of H. pylori appeared to decrease with increasing severity of the gastric lesion. In conclusion, it is suggested that non-invasive serological evaluation of anti-H. pylori (IgG) status after eradication therapy for peptic ulcer disease could be extended, after proper assessment of cut-off values and their validation, to the follow-up of patients with CG and IM.

Adult↗
PubMed2002

Prediction of chromatographic retention, pKa values and optimization of the separation of polyphenolic acids in strawberries.

Polyphenolic acids are a complex group of compounds that have attracted enormous attention in the last few years because of their biological properties. In this work, the proportion of organic modifier and the pH of acetonitrile-water mixtures used as mobile phases were optimized in order to separate a series of polyphenolic compounds. The linear solvation energy relationship formalism based on the single solvent polarity parameter, E(T)N was used to predict their chromatographic behavior as a function of the percentage of acetonitrile in the eluent. Moreover, the correlation established between retention and the pH of the aqueous-organic mobile phase was used to optimize the pH of the mobile phase. The optimized mobile phase is composed of acetonitrile and formic acid buffer adjusted to pH 4.25, with 12% (v/v) acetonitrile. Also, the pKa values of polyphenolic acids in acetonitrile-water mixtures were determined using chromatographic data, and in order to validate the optimized conditions, a series of polyphenolic compounds was studied in strawberries.

Fruit↗
PubMed2002

Liquid chromatography-mass spectrometry and capillary electrophoresis combined approach for separation and characterization of multicomponent peptide mixtures. Application to crude products of leuprolide synthesis.

A sequential combination of reversed-phase liquid chromatography-mass spectrometry (LC-MS) and capillary electrophoresis (CE) has been explored in order to perform separation and characterization of a multicomponent peptide mixture from the synthesis of leuprolide. The mixture was first analyzed and fractionated by LC-MS, and the collected fractions were subsequently separated by CE. Unambiguous identification of the electrophoretic peaks was achieved by injecting the collected fractions separately and spiking the leuprolide crude mixture. Furthermore, structural information about the components of the mixture provided by several semi-empirical migration models has been used to check the accuracy of the structures previously proposed by LC-MS. Combination of the two orthogonal techniques results in an enhancement of their individual selectivity characteristics.

Chromatography, Liquid↗
PubMed2002

Determination of difloxacin and sarafloxacin in chicken muscle using solid-phase extraction and capillary electrophoresis.

This paper describes a method for residue analysis of difloxacin and sarafloxacin in chicken muscle. Clean-up and preconcentration of the samples are effected by solid-phase extraction (C18) and the determination is carried out by capillary electrophoresis using a photodiode array detection system. The method was validated with satisfying results. The calibration graphs are linear for difloxacin and sarafloxacin from 50 to 300 microg/kg. The limit of detection obtained for difloxacin and sarafloxacin are 10 and 25 microg/kg, respectively, which allows the detection of positive muscle samples at the required maximum residue limits of European Union.

Animals↗
PubMed2002

Analysis of quinolone residues in edible animal products.

A comprehensive review on the analysis of quinolone antibacterials is presented. The review covers most of the methods described for the determination of quinolone residues in edible animal products. Sample handling, chromatographic conditions and detection methods have been discussed. A summary of the most relevant information about the analytical procedures has been included.

4-Quinolones↗
PubMed2002

pKa values of peptides in aqueous and aqueous-organic media. Prediction of chromatographic and electrophoretic behaviour.

In the present work, models describing the effect of the pH on the chromatographic and electrophoretic behaviour for polyprotic peptides were compared. The proposed models can be simultaneously used for determination of dissociation constants and selection of the optimum pH for the separation of peptides, in water and acetonitrile-water mixtures widely used in liquid chromatography and in capillary electrophoresis. The models use the pH value measured in the acetonitrile-water mixture instead of the pH value in water and take into account the effect of the activity coefficients. They permit the determination of the acidity constants in the aqueous and hydro-organic mobile phase from chromatographic retention and electrophoretic migration measurements, respectively. The values obtained by both proposed techniques agree with the potentiometric values previously determined. The suitability of the proposed models for predicting chromatographic and electrophoretic behaviour of compounds studied from a limited number of experimental data was also compared. The separation between solutes by both techniques in a complex mixture can be easily predicted, making simple and rapid pH selection to achieve optimum separation.

Chromatography, Liquid↗
PubMed2002

Translocation of protein kinase C by halothane in cholinergic cells.

Protein kinase C (PKC) is a signal transducing enzyme that is an important regulator of multiple physiologic processes and a potential molecular target for volatile anaesthetic actions. However, the effects of these agents on PKC activity are not yet fully understood. Volatile anaesthetics increase intracellular calcium concentration ([Ca(2+)](i)) in a variety of cells, thus their effects on PKC activity may be indirect due to [Ca(2+)](i) increase. Alternatively, the anaesthetics could directly stimulate PKC activity. In order to distinguish these two possibilities in intact cells, we used a fully functional green fluorescent protein conjugated PKCbetaII (GFP-PKCbetaII) and confocal microscopy to evaluate the dynamic redistribution of PKC in living SN56 cells, a cholinergic cell line, in response to halothane. Halothane induced PKC translocation in SN56 cells transfected with GFP-PKCbetaII. This effect was not suppressed by dantrolene, a drug that blocks halothane-induced Ca(2+) release from intracellular stores in these cells. These findings indicate that halothane induces PKC translocation in SN56 cells independently of its ability to release calcium from internal stores.

Anesthetics, Inhalation↗
PubMed2001

Halothane-induced intracellular calcium release in cholinergic cells.

Low concentrations of halothane and isoflurane can release acetylcholine in an extracellular Ca(2+)-independent manner. In the present study, a cholinergic cell line (SN56) was used to examine whether release of calcium from intracellular stores occurs in the presence of halothane. Changes in intracellular calcium concentration ([Ca(2+)](i)) were measured using fluo-3, a fluorescent calcium-sensitive dye and laser scanning confocal microscopy. Halothane, at sub-anesthetic concentrations (14, 28, 40 and 56 microM), increased [Ca(2+)](i) in SN56 cells. This effect remained even when the cells were perfused with medium lacking extracellular calcium, suggesting the involvement of intracellular Ca(2+) sources. SN56 cells responded to ryanodine by increasing [Ca(2+)](i) and this effect was blocked by dantrolene, an inhibitor of Ca(2+)-release from ryanodine-sensitive stores. The effect of halothane was attenuated after the increase in [Ca(2+)](i) induced by ryanodine and it was suppressed by dantrolene, suggesting the participation of ryanodine-sensitive stores. Using cyclopiazonic acid, a Ca(2+)-ATPase inhibitor, we investigated whether the depletion of intracellular Ca(2+) stores interfered with the effect of halothane. Cyclopiazonic acid significantly decreased the increase in [Ca(2+)](i) induced by the volatile anesthetic. It is suggested that sub-anesthetic concentrations of halothane may increase [Ca(2+)](i) by releasing Ca(2+) from intracellular stores in cholinergic cells.

Acetylcholine↗