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Biomedical subjects

M B Martins

Publications and source records attributed to M B Martins.

12 recordsLinked to original sources
PubMed2007

Occupational exposure in nuclear medicine in Portugal in the 1999-2003 period.

The annual doses received by the staff of nuclear medicine departments from public hospitals and private clinics and evaluated by the Individual Monitoring Service of the Radiological Protection and Nuclear Safety Department (DPRSN) of the Nuclear and Technological Institute (ITN) in Portugal, in the 5 y period from 1999 to 2003, are analysed and presented in this paper. In the 1999-2003 period, ITN-DPRSN monitored on an average 462 workers from nuclear medicine departments, which represents 6% of the 8000 workers of the medical field (approximately). The medical sector represents 80-85% of all the monitored population in Portugal. The professions of the monitored workers at nuclear medicine departments were identified by the respective departments as administrative, auxiliary, medical doctor, nuclear medicine technician, nurse, pharmacist and physicist. This information was collected at the onset of the monitoring and was updated over the last 3 y. The annual whole-body doses evaluated in the period 1999-2003 were used to derive the distribution of workers by dose intervals for every profession. The respective annual average doses and annual collective doses, as well as, the total average and total collective doses for the nuclear medicine sector were also determined and are presented. Internal radiation hasn't been monitored.

Body Burden↗
PubMed2006

Quantitative trait analysis and geographic variability of natural populations of Zaprionus indianus, a recent invader in Brazil.

Five natural samples of a recent South America invader, the drosophilid Zaprionus indianus, were investigated with the isofemale line technique. These samples were compared to five African mainland populations, investigated with the same method. The results were also compared to data obtained on mass cultures of other populations from Africa and India. Three quantitative traits were measured on both sexes, wing and thorax length and sternopleural bristle number. We did not find any latitudinal trend among the American samples, while a significant increase in body size with latitude was observed in the Indian and, to a lesser degree, in the African populations. American populations were also characterized by their bigger size. Genetic variability, estimated by the intraclass correlation among isofemale lines, was similar in American and African populations. The intraline, nongenetic variability was significantly less in the American samples, suggesting a better developmental stability, the origin of which is unclear. A positive relationship was evident between intraline variability of size traits and the wing-thorax length correlation. Altogether, our data suggest that the colonizing propagule introduced to Brazil had a fairly large size, preventing any bottleneck effect being detected. The big body size of American flies suggests that they came from a high-latitude African country. The lack of a latitudinal dine in America seems to be related to the short time elapsed since introduction. The very rapid spread of Z. indianus all over South America suggests that it might rapidly invade North America.

Animals↗
PubMed2004

Databases in use at the individual monitoring service of ITN-DPRSN.

In this work, the databases developed for routine use at the Individual Monitoring for External Radiation Service (IMS) of the Radiological Protection and Nuclear Safety Department (DPRSN) at the Nuclear and Technological Institute (ITN) in Portugal are presented. At the IMS there are two dosimetry systems running simultaneously, one based on film and the other one on thermoluminescent detectors (TLD). Two databases were initially and independently home-developed in order to meet each service's needs. A few modifications were introduced and while each service's requirements were maintained where needed, the databases were adapted in order to store the same type of information relative to the facilities and monitored workers, as well as to produce similar shaped reports and technical information. The necessary administrative features of the services were considered in the database development, made user-friendly and welcomed by the ordinary users. The improvements allowed a more direct analysis of the annual doses and an easy identification of professions and practices associated with higher dose values.

Academies and Institutes↗
PubMed2003

Design and characterization of enzymosomes with surface-exposed superoxide dismutase.

Superoxide dismutase (SOD) was chemically modified by covalent linkage of fatty acid chains to the accessible epsilon-amino groups of the enzyme. This acylation method gave rise to a different enzyme entity (Ac-SOD) as evidenced by different physicochemical properties such as octanol/water partition coefficient and isoelectric point (pI) as compared to SOD. Ac-SOD was incorporated in conventional and long-circulating liposomes (LCL) and characterized in terms of incorporation efficiency, protein to lipid ratio (Prot/Lip), enzymatic activity retention and zeta potential. The observation that Ac-SOD liposomes present enzymatic activity on their external surface indicates that these formulations can act independent of rate and extent of enzyme release as required in case of SOD liposomes. The decrease of superficial charge of liposomal formulations containing Ac-SOD, as compared to SOD liposomes, may be related to the negatively charged enzyme molecules localized on the liposome surface. The comparative characterization of Ac-SOD and SOD liposomal formulations evidenced that the two enzyme forms differ substantially regarding their intraliposomal location: SOD tends to be localized in the internal aqueous spaces, whereas Ac-SOD is expected to be localized in the lipid bilayers of the liposomes, partially buried into the outer surface and exposed to the external medium. These liposomal structures with surface-exposed SOD were designated as Ac-SOD enzymosomes. The properties of these enzymosomes may influence the therapeutic effect, as the release of the enzyme from extravasated vesicles is no longer a necessary requirement for achieving dismutating activity within the inflamed target site.

Acylation↗
PubMed2001

Occupational exposure in Portugal in 1999.

This study reports the occupational radiation doses for external exposure received in 1999 by the radiation workers monitored by the Radiological Protection and Nuclear Safety Department (DPRSN) in Portugal. Occupational exposures arise from conventional industry, research laboratories, the health or medical sector, and mining. There are no nuclear power plants in the country. There are two dosimetry systems running simultaneously at DPRSN, one based on film dosimetry and the other on thermoluminescence dosimetry (TLD). In 1999, 8400 persons were monitored, 3100 with film and 5300 with TLD and the data presented in this report were obtained by using both technologies. The annual mean effective doses received from external radiation in the different fields of activity and the distribution of the annual effective dose by dose intervals are presented. The collective annual dose by field of activity is estimated and the contribution to the total annual collective dose is determined.

Air Pollutants, Radioactive↗
PubMed1997

An analytical methodology to quantify the incorporation of enzymes in polyalkylcyanoacrylate nanoparticles based on size exclusion chromatography.

The performances of different methods of quantification of protein (methods based on direct spectrophotometric and spectrofluorimetric analysis, chemical reactions and liquid chromatography) to quantify the amount of enzyme incorporated into polyalkylcyanoacrylate nanoparticles, were compared. A methodology based on size exclusion chromatography was selected. The performances of the analytical method to quantify the enzymes L-asparaginase and superoxide dismutase in different polymerization media of poly-isobutilcyanoacrylate, were evaluated. The quantification of superoxide dismutase in the presence of esterase, enzyme used to solubilize nanoparticles, was attempted. An adequate separation between enzyme and the other components of polymerization media was achieved, so the selectivity of the method is adequate to the quantification of an enzyme in polymerization medium, either before or after polymerization. Although lack of selectivity of the column to separate enzymes was observed. The retention time of L-asparaginase and superoxide dismutase in polymerization medium are, respectively, 7.4 and 7.5. Linear correlation between peak area and enzyme concentration were observed for both enzymes in the concentration range from 10 to 80 micrograms ml-1, either before or after polymerization and in different polymerization media. This SE-HPLC analytical methodology is adequate to determine the degree of incorporation of enzymes in polyalkylcyanoacrylate nanoparticles as evidenced by the linear responses of the chromatographic method, the reproductibility of repeated sample injections and the precision of the quantification of enzyme concentration.

Asparaginase↗
PubMed1995

Yeast succession in the Amazon fruit Parahancornia amapa as resource partitioning among Drosophila spp.

The succession of yeasts colonizing the fallen ripe amapa fruit, from Parahancornia amapa, was examined. The occupation of the substrate depended on both the competitive interactions of yeast species, such as the production of killer toxins, and the selective dispersion by the drosophilid guild of the amapa fruit. The yeast community associated with this Amazon fruit differed from those isolated from other fruits in the same forest. The physiological profile of these yeasts was mostly restricted to the assimilation of a few simple carbon sources, mainly L-sorbose, D-glycerol, DL-lactate, cellobiose, and salicin. Common fruit-associated yeasts of the genera Kloeckera and Hanseniaspora, Candida guilliermondii, and Candida krusei colonized fruits during the first three days after the fruit fell. These yeasts were dispersed and served as food for the invader Drosophila malerkotliana. The resident flies of the Drosophila willistoni group fed selectively on patches of yeasts colonizing fruits 3 to 10 days after the fruit fell. The killer toxin-producing yeasts Pichia kluyveri var. kluyveri and Candida fructus were probably involved in the exclusion of some species during the intermediate stages of fruit deterioration. An increase in pH, inhibiting toxin activity and the depletion of simple sugars, may have promoted an increase in yeast diversity in the later stages of decomposition. The yeast succession provided a patchy environment for the drosophilids sharing this ephemeral substrate.

Animals↗
PubMed1994

Clonal rearrangements in human irradiated fibroblasts.

The cytogenetic dose response following in vivo localized irradiation is difficult to establish because of the occurrence of clones defined by chromosome alterations, with various proliferative rates. The biological meaning of these clones is not well understood. Two sets of experiments were performed to follow their behavior. R-banded karyotypes were established on human fibroblasts irradiated either before or after initiation of the cultures. Clones were observed in cultures developed after irradiation of biopsies, whereas irradiated cultures exhibited karyotypes with multiple non-clonal rearrangements. This difference suggests that most radiation-induced chromosome anomalies do not confer a selective advantage on the carrier cells in vitro. The appearance of clonal anomalies following biopsy irradiation would rather be a consequence of a strong selection at the time of the growth of the cells out of the explants, which would give rise to the progeny of a limited number of progenitor cells.

Cell Line, Transformed↗
PubMed1993

Specific chromosome instability induced by heavy ions: a step towards transformation of human fibroblasts?

Cultures of human skin fibroblasts were exposed to heavy ions: neon (E = 10.74 MeV/u) and argon (E = 10.52 MeV/u) at fluences of 10(6), 2 x 10(6) and 4 x 10(6) and lead (E = 9.5 MeV/u) at a fluence of 2 x 10(6) particles/cm2. Cultures were further prolonged for up to 25 passages and karyotyping was performed at various times. Radiation-induced chromosome anomalies progressively decreased, became quite rare at passages 5-7 and increased at later passages. Around passages 20-25, most anomalies occurring were dicentrics, involving telomeric regions of 13p and q arms principally and to a lesser degree those of 1p, 16p and 16q arms. These non-random rearrangements paralleled the appearance of clones with unbalanced karyotypes. In particular, two independent proliferating clones were characterized by a monosomy 13. It is concluded that most chromosome lesions directly induced by heavy ions are hardly compatible with cell survival and thus disappear after a few cell generations. However, surviving cells acquire a de novo chromosome instability leading to the formation of clones with unbalanced karyotypes at late passages.

Argon↗
PubMed1990

Acylation of L-asparaginase with total retention of enzymatic activity.

Acylation of L-asparaginase (L-asparagine amidohydrolase, EC 3.5.1.1) with complete retention of catalytic activity was achieved. Several parameters of the acylation method, based on the binding of palmitoyl residues to epsilon-NH2 groups of protein, were optimized. The correlation between the acylation degree of L-asparaginase and the retention of catalytic activity was established. For a palmitoyl chloride/protein molar ratio ranging from 50 to 900, a degree of modification of 10 to 30% and a retention of catalytic activity of 98 to 60% respectively, was observed. Hydrophobicity of 30% acylated protein was correlated with turbidity in water and octanol and was compared with the native protein. Acylated protein incorporated into liposomes, showed an increase in catalytic activity in intact form as compared to the native enzyme. By the introduction of a sequential acylation cycle, an improvement of the degree of modification with a maximal value at 50% was obtained. Total retention of catalytic activity was achieved by acylation in the presence of 8 mM L-asparagine in a reactional medium.

Acylation↗
PubMedDate not supplied

Biochemical characterization of an L-asparaginase bioconjugate.

In this work is characterized a bioconjugate of L-asparaginase, obtained by linkage of palmitic acid chains to the native enzyme in the presence of substrate as a protein protective molecule. Comparisons between isoelectric points, hydrophobicity, pH, and temperature profiles for the bioconjugate and the native enzyme were performed. A shift of pI from 5.03 to 4.58 was observed after conjugation. The modified enzyme evidences a 10-fold increase of the hydrophobicity. A small shift from 7.5 to 7 of the pH for maximal catalytic activity and a 5 degree C increase of temperature for maximal activity were observed with conjugation. Stability studies in human serum and on storage evidence similar behaviors for both bioconjugate and native enzyme. The retention of catalytic activity of the bioconjugate is dependent on the presence of micelles. The bioconjugate evidenced 65% retention of activity when catalytic activity was assayed without a surfactant and 98-100% retention of activity when catalytic activity was assayed in the presence of surfactant micelles. The kinetic characteristics of the bioconjugate and of the native enzyme, in micelles of different hydrophobicities, were compared. The Michaelis constant of native enzyme is 0.030 mM, independent of the surfactant, and the Michaelis constant of the bioconjugate varies with the surfactant, from 0.036 to 0.046 mM.

Asparaginase↗