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Biomedical subjects

J Martins

Publications and source records attributed to J Martins.

At least 19 recordsLinked to original sources
PubMed2006

Phototactic behavior in Daphnia magna Straus as an indicator of toxicants in the aquatic environment.

In this study, the phototactic behavior of Daphnia magna was investigated as a possible bioindicator for the following 11 chemicals commonly found in the aquatic environment: benzo(b)fluoranthene, mercury (II) chloride, dimethoate, lindane, linuron, MCPA, TBTO, carbon tetrachloride, thiram, 2,4,6-trichlorophenol and arsenic trioxide. Phototactic response was monitored as the movement of 7 to 8 day-old D. magna individuals. The analysis was carried out using glass test tubes divided radially into two zones, with increasing distance from a light source. For each of the compounds, different concentrations and exposure times were analyzed, and the behavior of the D. magna in each of the treatments compared to the controls in which the chemicals were not added. Using the experimental model described here, all of the 11 chemicals could be detected following exposure times of between 15 min and 48 h. The lowest concentrations detected using this technique were between 2 and 43 times lower than the LC(50) and EC(50) values reported for D. magna. The results of this study show that the analysis of phototactism is a useful method for detecting the presence of a wide range of potentially toxic chemicals found in the aquatic environment.

2-Methyl-4-chlorophenoxyacetic Acid↗
PubMed2006

[Temperature dialysate and hemodialysis tolerance].

In this study, the effect of dialysate temperature on hemodynamic stability, patients' perception of dialysis discomfort and postdialysis fatigue were assessed. Thirty-one patients of the morning shift were eligible to participate in the study. Three patients refused. Patients were assessed during 6 dialysis sessions: in three sessions the dialysate temperature was normal (37 degrees C) and in other three sessions the dialysate temperature was low (35.5 degrees C). To evaluate the symptoms along the dialysis procedure and the postdialysis fatigue, specific scale questionnaires were administered in each dialysis session and respective scores were elaborated. Low temperature dialysate was associated with higher postdialysis systolic blood pressure (122 +/- 24 vs. 126 +/- 27 mmHg, p < 0.05), and lower postdialysis heart rate (82 +/- 13 vs. 78 +/- 9 beats/min, p < 0.05) with the same ultrafiltration rate. Dialysis symptoms score and postdialysis fatigue score were better with the low dialysate temperature (0.7 +/- 0.9 vs. 0.4 +/- 1 vs. p < 0.05, and 1.3 +/- 1 vs. 1 +/- 0.9 p < 0.05, respectively). Furthermore, low temperature dialysate shortened the post-dialysis fatigue period (5.4 +/- 6.3 vs. 3.1 +/- 3.3 vs. hours, p < 0.05). The clinical improvement experimented with the low temperature dialysate was not universal. A beneficial effect was exclusively observed in the patients with higher dialysis symptoms and postdialysis fatigue scores or having more than one episode of hypotension in a week. The patients were asked about their temperature preference, 7 patients (23%) request a dialysate at 37 degrees C, 19 patients (61%) prefered to be dialysed with the low temperature dialysate, and 5 patients (16%) were indifferent. The later two groups of the patients continued with the low temperature dialysate during other 4 weeks. At the end of that period, the clinical improvement remained unchanged. In summary, low temperature dialysate is particularly beneficial for highly symptomatic patients.

Adult↗
PubMed2001

The molecular mechanism of lead inhibition of human porphobilinogen synthase.

Human porphobilinogen synthase (PBGS) is a main target in lead poisoning. Human PBGS purifies with eight Zn(II) per homo-octamer; four ZnA have predominantly nonsulfur ligands, and four ZnB have predominantly sulfur ligands. Only four Zn(II) are required for activity. To better elucidate the roles of Zn(II) and Pb(II), we produced human PBGS mutants that are designed to lack either the ZnA or ZnB sites. These proteins, MinusZnA (H131A, C223A) and MinusZnB (C122A, C124A, C132A), each become purified with four Zn(II) per octamer, thus confirming an asymmetry in the human PBGS structure. MinusZnA is fully active, whereas MinusZnB is far less active, verifying an important catalytic role for ZnB and the removed cysteine residues. Kinetic properties of the mutants and wild type proteins are described. Comparison of Pb(II) inhibition of the mutants shows that ligands to both ZnA and ZnB interact with Pb(II). The ZnB ligands preferentially interact with Pb(II). At least one ZnA ligand is responsible for the slow tight binding behavior of Pb(II). The data support a novel model where a high affinity lead site is a hybrid of the ZnA and ZnB sites. We propose that the lone electron pair of Pb(II) precludes Pb(II) to function in PBGS catalysis.

Amino Acid Substitution↗
PubMed2001

Mechanistic implications of mutations to the active site lysine of porphobilinogen synthase.

Porphobilinogen synthase (PBGS) is a homo-octameric protein that catalyzes the complex asymmetric condensation of two molecules of 5-aminolevulinic acid (ALA). The only characterized intermediate in the PBGS-catalyzed reaction is a Schiff base that forms between the first ALA that binds and a conserved lysine, which in Escherichia coli PBGS is Lys-246 and in human PBGS is Lys-252. In this study, E. coli PBGS mutants K246H, K246M, K246W, K246N, and K246G and human PBGS mutant K252G were characterized. Alterations to this lysine result in a disabled but not totally inactive protein suggesting an alternate mechanism in which proximity and orientation are major catalytic devices. (13)C NMR studies of [3,5-(13)C]porphobilinogen bound at the active sites of the E. coli PBGS and the mutants show only minor chemical shift differences, i.e. environmental alterations. Mammalian PBGS is established to have four functional active sites, whereas the crystal structure of E. coli PBGS shows eight spatially distinct and structurally equivalent subunits. Biochemical data for E. coli PBGS have been interpreted to support both four and eight active sites. A unifying hypothesis is that formation of the Schiff base between this lysine and ALA triggers a conformational change that results in asymmetry. Product binding studies with wild-type E. coli PBGS and K246G demonstrate that both bind porphobilinogen at four per octamer although the latter cannot form the Schiff base from substrate. Thus, formation of the lysine to ALA Schiff base is not required to initiate the asymmetry that results in half-site reactivity.

Amino Acid Substitution↗
PubMed2001

Molecular mechanism of lateral diffusion of py(10)-PC and free pyrene in fluid DMPC bilayers.

From the study of the kinetics of the fluorescence self-quenching of pyrene in multilamellar vesicles of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) in the fluid phase we obtain the molecular diffusion parameters, diffusion coefficients, and activation energies for lateral diffusion for three probes: 1-palmitoyl-2-(1-pyrenedecanoyl)-sn-glycero-3-phosphocholine (py(10)-PC), pyrene, and 1-pyrenebutanoic acid (py-but). The experiments are done in a range of temperatures for which the reversibility of excimer formation is negligible and the probe/phospholipid ratios used are low, avoiding non-ideal mixing of the probe. The time-resolved fluorescence decays are, in all cases, accurately and consistently described by the two-dimensional (2D) formalism for bimolecular diffusion-controlled reactions. From the parameters obtained in this way we conclude that the primary step of the diffusion of the pyrene-labeled phospholipid involves the simultaneous jump of phospholipid and fluorophore moieties, and also that although in the case of py(10)-PC the pyrene from molecules pertaining to different layers may interact during the lifetime of the exited state, this is not the case for free pyrene.

Biophysical Phenomena↗
PubMed2001

Immobilisation on polystyrene of diazirine derivatives of mono- and disaccharides: biological activities of modified surfaces.

The potential of surface glycoengineering for biomaterials and biosensors originates from the importance of carbohydrate-protein interactions in biological systems. The strategy employed here utilises carbene generated by illumination of diazirine to achieve covalent bonding of carbohydrates. Here, we describe the synthesis of an aryl diazirine containing a disaccharide (lactose). Surface analysis techniques [X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectroscopy (ToF-SIMS)] demonstrate its successful surface immobilisation on polystyrene (PS). Results are compared to those previously obtained with an aryl diazirine containing a monosaccharide (galactose). The biological activity of galactose- or lactose-modified PS samples is studied using rat hepatocytes, Allo A lectin and solid-phase semi-synthesis with alpha-2,6-sialyltransferase. Allo A shows some binding to galactose-modified PS but none to lactose-modified surfaces. Similar results are obtained with rat hepatocytes. In contrast, sialylation of lactose-modified PS is achieved but not with galactose-modified surfaces. The different responses indicate that the biological activity depends not only on the carbohydrate per se but also on the structure and length of the spacer.

Animals↗
PubMed2001

Antiarrhythmic drug use in the implantable defibrillator arm of the Antiarrhythmics Versus Implantable Defibrillators (AVID) Study.

BACKGROUND: Previous retrospective or observational series suggest that many patients with an implantable cardioverter-defibrillator (ICD) will be treated with antiarrhythmic drugs (AADs) to modify the frequency or manifestation of recurrent ventricular arrhythmias. The relative clinical benefit, however, is uncertain, and deleterious interactions can occur. The objective of this clinical investigation was to study the need for, and effects of, concomitant AAD use with the ICD in a prospectively defined cohort. METHODS: All patients randomly assigned to the ICD arm of the Antiarrhythmics Versus Implantable Defibrillators (AVID) study were followed for the addition of class I or III AADs ("crossover") after hospital discharge. Addition of AADs was strictly regulated by AVID protocol. The timing and reasons for crossover and the effects on ventricular arrhythmia recurrence were analyzed. Patients were excluded if they required AADs before hospital discharge after index arrhythmias or if they had no ventricular arrhythmia before initiation of AADs. RESULTS: After a median follow-up of 135 days, 81 (18%) of the 461 eligible patients required AADs and formed the crossover group. The primary reason for crossover was frequent ICD shocks in 64% of patients. The most common AAD selected was amiodarone (in 42%). Independent predictors of crossover were lower ejection fraction, absence of ventricular fibrillation, or presence of nonsyncopal ventricular tachycardia at presentation, prior unexplained syncope, female sex, and history of cigarette smoking. Before AAD use, the 1-year arrhythmia event rate was 90%; after AAD, the event rate was only 64% (P =.0001). The time to first event was extended from 3.9 +/- 0.7 months to 11.2 +/- 1.8 months. There were 1.4 +/- 3.7 fewer ICD therapy events (P =.005) after crossover, predominantly accounted for by reduction in shocks rather than antitachycardia pacing therapies. CONCLUSIONS: The majority of patients who receive ICDs for sustained ventricular tachycardia or ventricular fibrillation can be treated without AADs. Most commonly, AADs are added to combat frequent ICD shocks, which are successfully reduced by AAD therapy.

Aged↗
PubMed2001

Neural networks and logical reasoning systems: a translation table.

A correspondence is established between the basic elements of logic reasoning systems (knowledge bases, rules, inference and queries) and the structure and dynamical evolution laws of neural networks. The correspondence is pictured as a translation dictionary which might allow to go back and forth between symbolic and network formulations, a desirable step in learning-oriented systems and multicomputer networks. In the framework of Horn clause logics, it is found that atomic propositions with n arguments correspond to nodes with nth order synapses, rules to synaptic intensity constraints, forward chaining to synaptic dynamics and queries either to simple node activation or to a query tensor dynamics.

Logic↗
PubMed2000

Porphobilinogen synthase from pea: expression from an artificial gene, kinetic characterization, and novel implications for subunit interactions.

Porphobilinogen synthase (PBGS) is present in all organisms that synthesize tetrapyrroles such as heme, chlorophyll, and vitamin B(12). The homooctameric metalloenzyme catalyzes the condensation of two 5-aminolevulinic acid molecules to form the tetrapyrrole precursor porphobilinogen. An artificial gene encoding PBGS of pea (Pisum sativum L.) was designed to overcome previous problems during bacterial expression caused by suboptimal codon usage and was constructed by recursive polymerase chain reaction from synthetic oligonucleotides. The recombinant 330 residue enzyme without a putative chloroplast transit peptide was expressed in Escherichia coli and purified in 100-mg quantities. The specific activity is protein concentration dependent, which indicates that a maximally active octamer can dissociate into less active smaller units. The enzyme is most active at slightly alkaline pH; it shows two pK(a) values of 7.4 and 9.7. Atomic absorption spectroscopy shows maximal binding of three Mg(II) per subunit; kinetic data support two functionally distinct types of Mg(II) and the third appears to be nonphysiologic and inhibitory. Analysis of the protein concentration dependence of the specific activity suggests that the minimal functional unit is a tetramer. A model of octameric pea PBGS was built to predict the location of intermolecular disulfide linkages that were revealed by nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis. As verified by site-specific mutagenesis, disulfide linkages can form between four cysteines per octamer, each located five amino acids from the C-terminus. These data are consistent with the protein undergoing conformational changes and the idea that whole-body motion can occur between subunits.

Amino Acid Sequence↗
PubMed2000

An artificial gene for human porphobilinogen synthase allows comparison of an allelic variation implicated in susceptibility to lead poisoning.

Porphobilinogen synthase (PBGS) is an ancient enzyme essential to tetrapyrrole biosynthesis (e.g. heme, chlorophyll, and vitamin B(12)). Two common alleles encoding human PBGS, K59 and N59, have been correlated with differential susceptibility of humans to lead poisoning. However, a model for human PBGS based on homologous crystal structures shows the location of the allelic variation to be distant from the active site with its two Zn(II). Previous microbial expression systems for human PBGS have resulted in a poor yield. Here, an artificial gene encoding human PBGS was constructed by recursive polymerase chain reaction from synthetic oligonucleotides to rectify this problem. The artificial gene was made to resemble the highly expressed homologous Escherichia coli hemB gene and to remove rare codons that can confound heterologous protein expression in E. coli. We have expressed and purified recombinant human PBGS variants K59 and N59 in 100-mg quantities. Both human PBGS proteins purified with eight Zn(II)/octamer; Zn(II) binding was shown to be pH-dependent; and Pb(II) could displace some of the Zn(II). However, there was no differential displacement of Zn(II) by Pb(II) between K59 and N59, and simple Pb(II) inhibition studies revealed no allelic difference.

Alleles↗
PubMed1999

Variation of infrarenal aortic diameter: A necropsy study.

PURPOSE: To determine anatomicomorphological changes in the infrarenal portion of the abdominal aorta, we performed 645 dissections of the segment in corpses undergoing necropsy. METHODS: The aortas were removed from the corpses with a surgical technique; by means of a device that we designed, the external diameter of the artery was measured after luminal pressure was reestablished. This way, it was possible to avoid underestimation of the arterial diameter postmortem. The influence of age, sex, body size, arterial hypertension, chronic obstructive pulmonary disease, and coronary disease on the aortic diameter and the influence of different degrees of sclerosis on the infrarenal aorta wall were analyzed. Considering the diameters, aortas were regarded as "normal" when they did not present any ectasia, arteriomegaly, aneurysm, or hypoplasia. RESULTS: The sample involved 645 subjects whose ages ranged from 19 to 97 years (mean age, 55.8 years). Of the 645 subjects, 65.5% (423) were men, 34.5% (222) were women, 81% (523) were white, and 19% (122) were of another race. The diameters of arteries showing no anomalous dilatation (ectasis, arteriomegaly, or aneurysm) varied according to subject age, sex, body length, and the degree of atherosclerosis on the aorta wall (P <.01). Aortic diameters of those subjects with arterial hypertension, coronary disease, and chronic obstructive pulmonary disease were compared with the aortic diameters of control subjects, and significant differences were not shown (P >.05). Twenty-nine aneurysms were found (4.5% prevalence). Four were ruptured aneurysms, and all occurred in aortas with diameters larger than 5.0 cm. CONCLUSION: The infrarenal aortic diameter enlarges with aging, and this enlargement occurs earlier in men than in women. Those subjects who had a longer body length and advanced sclerosis on the aorta wall had larger aortic diameters. There was a high prevalence of infrarenal aneurysms (4.5%), with rupture found solely in aortas with diameters larger than 5.0 cm.

Adult↗
PubMed1998

Childhood and adolescent changes of skeletal relationships.

This paper describes the development of anteroposterior (AP) and vertical (VER) skeletal relationships. A mixed-longitudinal sample of 49 females and 50 males was followed during childhood and adolescence. Childhood growth changes were assessed from 6 to 10 years for females and 8 to 12 years for males. Adolescent changes were evaluated from 9 to 13 years for females and 11 to 15 years for males. Anteroposterior relationships were described by the horizontal distance between ANS and Pg. Vertical relationships were described by the vertical distance between Pg and Go. Subsamples were defined based on overall changes (AP and VER) that were either greater than or less than average. The results showed that AP and VER relationships were not stable during growth. AP relationships changed over time due to differential growth movements of the mandible (as opposed to the maxilla). There was greater potential for horizontal discrepancies to decrease during childhood than during adolescence. The potential for AP discrepancies to increase was greater during adolescence. The VER relationships increased in the majority of subjects. The subsample whose vertical discrepancies increased most showed less inferior movement of gonion and more inferior movement of pogonion. Inferior movements of Pg and Go were greater during adolescence than childhood.

Adolescent↗
PubMed1995

[ERCP/ES in the therapy of acute calculous pancreatitis].

In the medical press there are several data confirming the value of E.R.C.P. and E.E.S., in the therapeutical approach of acute lithiasic pancreatitis (A.L.P.). Nowadays it is a first line endoscopic technic on the therapeutical approach in A.L.P. permitting to clean out the biliary tree of stones, eliminating the etiological factor of the disease. It's the experience of the group of E.R.C.P./E.S.E. of Hospital dos Capuchos that we will present on this paper.

Acute Disease↗
PubMed1990

Obstetric risks and outcomes: birth centre compared with conventional labour ward.

Birth centres in Australia provide an option for women and their professional advisors when choosing the setting for childbirth. It is important that empirical information about the risks is available to enable informed decisions to be made. The purpose of this study was to compare the obstetric outcomes for women admitted to the Birth Centre at Royal Hospital for Women in Sydney with outcomes for women admitted to the conventional labour ward, controlling for prenatal and intrapartum risk. The findings indicate that, with the existing back-up provided by the conventional service, the outcomes for women admitted to the Birth Centre were at least as good as those of the other women. The study also shows that there are differences between the two settings in the management of the intrapartum period. The rate of intervention is substantially higher for women admitted to the Labour Ward, after risk is taken into consideration. The evaluation indicates that the Birth Centre offers a viable choice for women with relatively low obstetric risk.

Delivery Rooms↗
PubMed1990

[Phenomenology as a methodological alternative for research: some considerations].

The authors present the fundamental ideas of the phenomenology as an epistemology aiming human sciences which is concerned with the past experiences of the subjects and necessarily uses reflection as a way to consider the facts as they show up. As a methodological alternative for research, the phenomenology seeks the essence of the posed phenomenon and, to analyse its structure the investigator gets descriptions of the subjects who undergo the situation, aiming the formation of significant units. Hermeneutics is a kind of interpretation which must rely on a philosophical body of experience.

Humans↗
PubMed1988

Obstetric high risk screening and prediction of neonatal morbidity.

A retrospective study using an obstetric risk score protocol was applied to a stratified sequential sample of 843 singleton livebirths, occurring in the Royal Hospital for Women, Sydney, over a 12-month period (March, 1985-February, 1986). Data collection included 53 prenatal factors, 41 intrapartum factors and 37 neonatal factors. The study was comprised of 346 women admitted to the hospital birth centre and 497 women admitted to labour ward. In labour ward admitted women there was a significant association between high prenatal scores, high intrapartum scores and high neonatal morbidity scores. Women admitted to the birth centre were subjected to a screening procedure which resulted in low prenatal and relatively low intrapartum risk scores. However, neonatal morbidity scores were similar for both groups. The risk scoring protocol used in this study requires further revision to allow the adequate selection of low risk women delivering infants with a low risk of neonatal morbidity in a low risk obstetric setting.

Australia↗