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Biomedical subjects

A M Almeida

Publications and source records attributed to A M Almeida.

At least 19 recordsLinked to original sources
PubMed2002

Linear regression for calibration lines revisited: weighting schemes for bioanalytical methods.

When the assumption of homoscedasticity is not met for analytical data, a simple and effective way to counteract the greater influence of the greater concentrations on the fitted regression line is to use weighted least squares linear regression (WLSLR). The purpose of the present paper is to stress the relevance of weighting schemes for linear regression analysis and to show how this approach can be useful in the bioanalytical field. The steps to be taken in the study of the linear calibration approach are described. The application of weighting schemes was shown by using a high-performance liquid chromatography method for the determination of lamotrigine in biological fluids as a practical example. By using the WLSLR, the accuracy of the analytical method was improved at the lower end of the calibration curve. Bioanalytical methods data analysis was improved by using the WLSLR procedure.

Calibration↗
PubMed2001

Lamotrigine analysis in blood and brain by high-performance liquid chromatography.

A reversed-phase high-performance liquid chromatography assay was developed and validated to determine plasma and brain lamotrigine concentrations allowing pharmacokinetic-pharmacodynamic studies of this new antiepileptic drug in patients and laboratory animals. Lamotrigine and its internal standard were extracted, under alkaline conditions, from plasma and brain homogenate, into ethyl acetate; brain proteins were previously precipitated with trichloroacetic acid. The method was linear between 0.1 and 15.0 mg/l for plasma, with a detection limit of 0.008 mg/l, and between 0.1 and 5.0 mg/l for brain homogenate, with a detection limit of 0.023 mg/l. The method proved to be simple, useful and appropriate, not only for clinical and experimental research, but also for routine monitoring of lamotrigine concentrations in patients.

Animals↗
PubMed2001

Neonatal screening for haemoglobinopathies: the results of a 10-year programme in an English Health Region.

Neonatal identification of sickle cell disease can significantly reduce mortality and morbidity during the first 5 years of life. During a 10-year period, 414,801 neonates were screened by isoelectric focusing. The most common variants detected were haemoglobins S, C, D and E. Two hundred and fifty of the samples tested were homozygotes or compound heterozygotes, and 6554 samples were heterozygotes for the common variants. The gene frequencies in the population tested were calculated from this data for the most common variants. They were: S, 0.0057; C, 0.0014; D(Punjab(Los Angeles)), 0.0007; E, 0.0005. Additionally, 16 babies had beta thalassaemia major and 405 had rarer variants, of which six had never previously been described. Knowledge of the distribution of these inherited diseases is useful in healthcare planning and appropriate allocation of resources, while counselling targeted at appropriate couples enables informed parental choice and may prevent disease.

Anemia, Sickle Cell↗
PubMed2000

Proton re-uptake partitioning between uncoupling protein and ATP synthase during benzohydroxamic acid-resistant state 3 respiration in tomato fruit mitochondria.

The yield of oxidative phosphorylation in isolated tomato fruit mitochondria depleted of free fatty acids remains constant when respiratory rates are decreased by a factor of 3 by the addition of n-butyl malonate. This constancy makes the determination of the contribution of the linoleic acid-induced energy-dissipating pathway by the ADP/O method possible. No decrease in membrane potential is observed in state 3 respiration with increasing concentration of n-butyl malonate, indicating that the rate of ATP synthesis is steeply dependent on membrane potential. Linoleic acid decreases the yield of oxidative phosphorylation in a concentration-dependent manner by a pure protonophoric process like that in the presence of FCCP. ADP/O measurements allow calculation of the part of respiration leading to ATP synthesis and the part of respiration sustained by the dissipative H(+) re-uptake induced by linoleic acid. Respiration sustained by this energy-dissipating process remains constant at a given LA concentration until more than 50% inhibition of state 3 respiration by n-butyl malonate is achieved. The energy dissipative contribution to oxygen consumption is proposed to be equal to the protonophoric activity of plant uncoupling protein divided by the intrinsic H(+)/O of the cytochrome pathway. It increases with linoleic acid concentration, taking place at the expense of ADP phosphorylation without an increase in the respiration.

Hydroxamic Acids↗
PubMed2000

Theophylline pharmacokinetics with concomitant steroid and gold therapy.

BACKGROUND: Theophylline has been used for several decades in the treatment of asthma. In recent years, however, with the appreciation of the importance of inflammation in the pathogenesis of asthma, new therapeutic approaches have arisen, including beta2-agonists, steroid and nonsteroidal anti-inflammatory drugs, such as gold salts. OBJECTIVE: In the present work we studied the kinetic behaviour of theophylline administered concomitantly with methylprednisolone (steroid compound) and auranofin (oral gold) in six adult female patients. METHOD: Drug concentration data for patients under routine care were collected. The kinetic analysis (Bayesian Approach) was done using two different commercial software packages, PKS (Abbott Diagnostics) and CAPCIL (SIMKIN Inc., courtesy of Dade-Behring). A one-compartment open model with first-order absorption (ka for PKS=0. 5/h; ka for CAPCIL=0.3/h ) and first- order elimination. Default CL, t1/2 and Vd values were used for each program was assumed. The measured and predicted theophylline concentrations were used to calculate percentage prediction errors defined as %PE=[(predicted conc. - measured conc.)/measured conc.] x 100. A linear regression analysis was also carried out for the observed concentrations and those predicted by each method (PKS vs. CAPCIL). RESULTS: The predicted concentrations indicating persistently over-predicted the observed theophylline serum levels (results expressed as median and interquartile range; %PE for PKS=58.1 [37.1-126.0]; %PE for CAPCIL=34.0 [12.5-93.8]). The regression analysis confirmed the same tendency, showing an intercept significantly different from zero using both PKS and CAPCIL. CONCLUSION: The results suggest a possible interaction between theophylline and auranofin. Both PKS and CAPCIL failed to predict theophylline serum levels based exclusively on population pharmacokinetic parameters. The lower observed concentrations than expected have obvious implications in practice. Periodic theophylline serum determinations are advisable until further studies provide the necessary clarification about the kinetic profile of theophylline in patients taking concomitant steroids and gold salts.

Adult↗
PubMed2000

The kinetic profile of gentamicin in premature neonates.

The kinetic profile of gentamicin in premature infants has been studied to enable the development of optimized dosage schedules for neonatal intensive-care units and to stress the relationship between the pharmacokinetic parameters and several demographic, developmental and clinical factors which might be associated with changes in gentamicin disposition. Sixty-eight newborn patients of 24- to 34-weeks gestational age and 600-3,100 g current weight in their first week of life, undergoing routine therapeutic drug monitoring of their gentamicin serum levels, were included in this retrospective analysis. Gentamicin pharmacokinetic parameters were determined through non-linear regression by using a single-compartment open model. By regression analysis the current weight (g) was shown to be the strongest co-variate, and both gentamicin clearance (L h(-1)) and volume of distribution (L) had to be normalized. Additionally, gentamicin clearance depended on gestational age with a cut-off at 30 weeks, which allowed the division of the overall population into two subsets (< 30 weeks and between 30-34 weeks of gestational age). The younger neonates (<30 weeks of gestational age) showed a lower gentamicin clearance (0.0288 vs 0.0340 L h(-1) kg(-1)), a slightly higher volume of distribution (0.464 vs 0.435 L kg(-1)), and a longer half-life (11.17 vs 8.88 h) compared with the older subgroup (30-34 weeks of gestational age). On the basis of the pharmacokinetic parameters obtained, we suggest loading doses of 3.7 and 3.5 mg kg(-1) for the two subgroups of neonates (<30 weeks and 30-34 weeks of gestational age), respectively. The appropriate maintenance doses in accordance with the characteristics of the patients should be 2.8 mgkg(-1)/24h and 2.6 mg kg(-1)/18 h for neonates < 30 weeks and between 30-34 weeks of gestational age, respectively. Finally, when compared with previous studies, the information obtained on the pharmacokinetics and determinants of the pharmacokinetic variability of gentamicin in neonates was shown to be consistent.

Age Factors↗
PubMed2000

The use of filter paper plasticized with polyvinyl alcohol-glutaraldehyde in ELISA.

F1-antigen purified from Yersinia pestis was covalently linked to 5-mm diameter filter paper discs plasticized with polyvinyl alcohol-glutaraldehyde. These discs were used both for ELISA and dot-ELISA for the detection of anti-F1 IgG in rabbits. The best conditions were achieved using 1.25 microg of F1 antigen/disc, 3% w/v skim milk in PBS as blocking agent, anti-IgG peroxidase conjugate diluted 12,000 times, and serum from rabbits immunized or not against Y. pestis, diluted 6,400 times. The absorbance values obtained from the comparative study between this procedure and conventional ELISA were not significantly different but the low cost of the reagents employed in ELISA using the filter paper discs plasticized with polyvinyl alcohol-glutaraldehyde makes this method economically attractive.

Animals↗
PubMed1999

Diphenylacetaldehyde-generated excited states promote damage to isolated rat liver mitochondrial DNA, phospholipids, and proteins.

This work studies damage to rat liver mitochondrial protein, lipid, and DNA caused by electronically excited states generated by cytochrome c-catalyzed diphenylacetaldehyde enol oxidation to triplet benzophenone. The extension of lipid peroxidation was estimated by production of thiobarbituric acid-reactive substances and by formation of Schiff bases with membrane proteins, evaluated by SDS-polyacrylamide gel electrophoresis. Concomitant with DPAA-driven mitochondrial permeabilization, extensive mtDNA fragmentation occurred and DNA adducts with aldehydes-products of fatty acid oxidation-were observed. The degree of lipid peroxidation and mtDNA alterations were significantly decreased by butylated hydroxytoluene, a potent peroxidation chain breaker. The lipid peroxidation process was also partially inhibited by the bioflavonoid rutin and urate totally prevented the mitochondrial transmembrane potential collapse. In all cases, the mitochondrial damage was dependent on the presence of phosphate ions, a putative bifunctional catalyst of carbonyl enolization. These data are consistent with the notion that triplet ketones may act like alkoxyl radicals as deleterious reactive oxygen species on biologic structures. Involvement of singlet dioxygen formed by triplet-triplet energy transfer from benzophenone in the model reaction with DPAA/cytochrome c in the presence of DCP liposomes was suggested by quenching of the accompanying chemiluminescence upon addition of histidine and lycopene.

Aldehydes↗
PubMed1998

Linoleic acid-induced activity of plant uncoupling mitochondrial protein in purified tomato fruit mitochondria during resting, phosphorylating, and progressively uncoupled respiration.

An uncoupling protein was recently discovered in plant mitochondria and demonstrated to function similarly to the uncoupling protein of brown adipose tissue. In this work, green tomato fruit mitochondria were purified on a self-generating Percoll gradient in the presence of 0.5% bovine serum albumin to deplete mitochondria of endogenous free fatty acids. The uncoupling protein activity was induced by the addition of linoleic acid during the resting state, and in the progressively uncoupled state, as well as during phosphorylating respiration in the presence of benzohydroxamic acid, an inhibitor of the alternative oxidase and with succinate (+ rotenone) as oxidizable substrate. Linoleic acid strongly stimulated the resting respiration in fatty acid-depleted mitochondria but had no effect on phosphorylating respiration, suggesting no activity of the uncoupling protein in this respiratory state. Progressive uncoupling of state 4 respiration decreased the stimulation by linoleic acid. The similar respiratory rates in phosphorylating and fully uncoupled respiration in the presence and absence of linoleic acid suggested that a rate-limiting step on the dehydrogenase side of the respiratory chain was responsible for the insensitivity of phosphorylating respiration to linoleic acid. Indeed, the ADP/O ratio determined by ADP/O pulse method was decreased by linoleic acid, indicating that uncoupling protein was active during phosphorylating respiration and was able to divert energy from oxidative phosphorylation. Moreover, the respiration rates appeared to be determined by membrane potential independently of the presence of linoleic acid, indicating that linoleic acid-induced stimulation of respiration is due to a pure protonophoric activity without any direct effect on the electron transport chain.

Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone↗
PubMed1998

Free fatty acids regulate the uncoupling protein and alternative oxidase activities in plant mitochondria.

Two energy-dissipating systems, an alternative oxidase and an uncoupling protein, are known to exist in plant mitochondria. In tomato fruit mitochondria linoleic acid, a substrate for the uncoupling protein, inhibited the alternative oxidase-sustained respiration and decreased the ADP/O ratio to the same value regardless of the level of alternative oxidase activity. Experiments with varying concentrations of linoleic acid have shown that inhibition of the alternative oxidase is more sensitive to the linoleic acid concentration than the uncoupling protein activation. It can be proposed that these dissipating systems work sequentially during the life of the plant cell, since a high level of free fatty acid-induced uncoupling protein activity excludes alternative oxidase activity.

Carrier Proteins↗
PubMed1998

Kinetic profile of carbamazepine in an adult Portuguese outpatient population.

OBJECTIVE: The aim of our work was to define the kinetic profile of carbamazepine (CBZ), in order to improve on dosing schedules through a Bayesian approach. METHOD: Carbamazepine dose/steady-state trough concentrations data pairs and associated information were collected retrospectively on a population of adult epileptic patients. RESULTS: Fifty patients (index population) with two or more available concentrations (total of 174 determinations) met our inclusion criteria. Patients were taking CBZ (200-1800 mg/day) in mono- or polytherapy regimens. The analysis assumed a one-compartmental model with first-order absorption and elimination. Due to the data source (only trough concentrations were measured as part of hospital routine), the volume of distribution was fixed at 1.19 l/kg. The final estimates for CL were: 0.075 +/- 0.027 (mono- and polytherapy), 0.069 +/- 0.020 (monotherapy), and 0.106 +/- 0.037 l/h/kg (polytherapy). In order to validate these results, we assessed their predictive capacity using 18 new patients (validation population), submitted to the same inclusion criteria and using Prediction-Error analysis. The results suggested a different CL value for our population compared to earlier published clearance values. The results also pointed to an increased metabolic rate associated with polytherapy. The prediction capacity of the optimization method derived from a Portuguese population made in an a priori evaluation indicated a low error (-0.04 microg/ml), close to the theoretical zero value. CONCLUSION: Our results provide specific data on CBZ disposition in a Portuguese population and given the wide variability in the literature values, our data may help improve dosing of CBZ in Portuguese patients.

Adult↗
PubMed1998

The kinetic profile of vancomycin in neonates.

The pharmacokinetic parameters of vancomycin in a neonatal population have been characterized to enable development of optimum dosage guidelines for neonatal intensive-care units and to examine the relationship between these pharmacokinetic parameters and various demographic, developmental and clinical factors which might be associated with changes in the kinetic profile of vancomycin. Forty-four infants (twenty-five males and nineteen females) with suspected or proven Gram-positive infection and who received intravenous vancomycin between October 1993 and December 1996 were included in this retrospective analysis. Gestational age ranged from 25 to 40 weeks and postconceptional age at the time of the study ranged from 28 to 45 weeks. Sixty case-studies were obtained from the forty-four patients, with one period of study corresponding to one week or one cycle of therapy. Vancomycin pharmacokinetic parameters were determined by use of a one-compartment model. By regression analysis the current weight (g) was shown to be the stronger covariate, and both vancomycin clearance (L h(-1)) and volume of distribution (L) had to be normalized. The vancomycin volume of distribution depended on the postconceptional age with a cut-off at 32 weeks, whereas vancomycin clearance depended on the presence or absence of concomitant treatment with indomethacin or of mechanical ventilation, or both. On the basis of the pharmacokinetic parameters obtained we suggest initial dosage guidelines for vancomycin ranging from 10 mg kg(-1) every 8 h to 10 mg kg(-1) every 12 h, depending on the demographic and clinical characteristics of the patients. The results obtained enabled application of better a priori and a posteriori dosage schedules to infants in neonatal intensive-care units by use of the Bayesian approach, although further prospective study is recommended before direct extrapolation to patients in other settings.

Body Weight↗
PubMed1996

Chemical and pharmacological characterization of halitoxin from Amphimedon viridis (Porifera) from the southeastern Brazilian coast.

The halitoxin complex from the marine sponge Amphimedon viridis, collected in the São Sebastião channel (southeastern Brazilian coast), was isolated by gel-filtration chromatography on Sephadex LH-20. Spectroscopic data (1H, 13C and 2D-NMR) of halitoxin from A. viridis indicated that it has the same two alkylpyridine monomers composition of the previously isolated halitoxin from Amphimedon compressa (as Haliclona rubens). Nevertheless, analysis by High Performance Gel Permeation Chromatography indicated that the halitoxin complex of A. viridis has a lower molecular weight (500, 2000 and 5000 Da; the major component corresponding to the fraction of 2000 Da MW) when compared to the previously isolated halitoxin complex from A. compressa. Some pharmacological properties of the halitoxin complex from A. viridis were evaluated in terms of lethality, antimitosis, hemolysis and neurotoxicity. The possible chemotaxonomic value of alkyl pyridine alkaloids is discussed.

Action Potentials↗
PubMed1996

Clinical-epidemiologic study of alopecia areata.

BACKGROUND: Alopecia areata is a common disease and may be associated with autoimmune disease, atopy, Down syndrome, emotional stress, and foci of sepsis. METHODS: Seven cases of alopecia areata were diagnosed among workers in the Water and Effluent Treatment Sector (WETS) of a paper factory, representing a 0.6% incidence, when the value for the population at large is 0.1%. Three of these workers are assigned to the WETS on a permanent basis and four provide maintenance services. One of the latter patients had alopecia areata that fully regressed. Because biologic treatment of water and effluents involves saprophytic bacteria and fungi as well as chemical substances such as acrylamide, a clinical examination and laboratory tests were performed on all workers assigned permanently to the WETS (N = 9) and on 25% of the workers, selected at random providing services to the sector (N = 14). RESULTS: There was no association between alopecia areata and atopy, dermatophytosis, or bacteria isolated. Toxicologic evaluation revealed an acrylamide-like substance in 7 workers with alopecia areata, with a statistically significant correlation. Measures were taken at the workplace to decrease worker contact with the mists (probably containing acrylamide) in the pulp-pressing room; no other cases of alopecia areata had been detected 1 year after the study. CONCLUSIONS: A survey of the literature did not show reports of alopecia areata as an occupational dermatosis, but our conclusion is, that this dermatosis could be due to the professional activities of the workers at the paper factory studied.

Adult↗
PubMed1994

Oxidative damage of mitochondria induced by Fe(II)citrate is potentiated by Ca2+ and includes lipid peroxidation and alterations in membrane proteins.

Isolated rat liver mitochondria exposed to Fe(II)citrate undergo lipid peroxidation and alterations in membrane proteins. These processes were associated with irreversible decrease in membrane potential and mitochondrial swelling. Lipid peroxidation was evidenced by the production of thiobarbituric acid-reactive substances and also by the reaction of these products with membrane proteins, through the formation of Schiff bases. Alterations in membrane proteins were also characterized by the loss of specific proteins that could be recovered from the mitochondrial supernatant as shown by SDS-polyacrylamide gel electrophoresis. The degree of both lipid peroxidation and alterations in membrane proteins were diminished by EGTA, ruthenium red, or dibucaine. This strongly indicates that Ca2+ potentiates the oxidative damage of mitochondria exposed to Fe(II)citrate.

Animals↗
PubMed1992

Identification of surface-exposed Yersinia pestis proteins by radio-iodination and biotinylation.

When whole cells (stationary phase) of Yersinia pestis strain EV76 were radiolabelled with Iodogen and 131I, 16 major and 10 minor surface-exposed outer membrane proteins (OMPs) were identified. Labelling with N-hydroxysuccinimidyl 6-biotinylamino-hexanoate (biotin X-NHS) resulted in a complex protein profile detectable after blotting and developing with peroxidase-conjugated avidin. Y. pestis cell fractionation revealed that biotin X-NHS labelled not only OMPs but also proteins of inner cell compartments. Therefore, radiolabelling was the more reliable technique for identifying the OMPs of Y. pestis.

Bacterial Outer Membrane Proteins↗