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Biomedical subjects

M Silva

Publications and source records attributed to M Silva.

At least 91 records · Page 5Linked to original sources
PubMed1997

Nucleolar dominance in triticales: control by unlinked genes.

Hybrid plants and animals often show suppression of activity of ribosomal genes (rDNA) originating from one of the parental or ancestral species. In the wheat x rye amphiploid triticale, containing 28 chromosomes of wheat origin and 14 from rye, rDNA of rye origin (on chromosome 1R) is not normally expressed, while the 1B- and 6B-origin rDNA from wheat shows strong expression. Expression of rDNA can be accurately assessed by the silver staining method, which stains both interphase nucleoli and metaphase rDNA sites that were actively expressed at the previous interphase. We show here that substitution of another rye chromosome, 2R, by a chromosome from hexaploid wheat, 2D (triticale-2D(2R)), prevents suppression of the rye-origin rDNA, and leads to activity of all six major rDNA loci. These results were found in two different triticales and supported by rDNA behaviour in wheat-rye chromosomal addition lines. Models for chromosomal interactions leading to control of rDNA expression are presented.

Chimera↗
PubMed1997

Apoptosis of human myeloid leukemia cells induced by an inhibitor of protein phosphatases (okadaic acid) is prevented by Bcl-2 and Bcl-X(L).

Okadaic acid, an inhibitor of serine/threonine protein phosphatases 1 and 2A has been shown to cause mitotic arrest and cell death of HL-60 and K562 cells. HL-60 cells express Bcl-2 and little or no Bcl-X(L), while K562 expresses Bcl-X(L) but not Bcl-2. Since phosphorylation/dephosphorylation reactions have been suggested to be involved in the regulation of Bcl-2, we planned to investigate whether the expression of Bcl-2, Bcl-X(L) and Bax, a protein that antagonizes the antiapoptotic function of Bcl-2, are regulated in myeloid leukemia cell lines (K562, KU812 and HL-60) treated with okadaic acid. Our results indicate that exposure of all three leukemic cell lines to nanomolar concentrations of okadaic acid causes a loss of viability by activation of an apoptotic process accompanied by a marked decrease in the expression of Bcl-2, Bcl-X(L) and Bax at both mRNA and protein level, but not of c-fos, vimentin and epsilon-globin, ruling out a non-specific effect of okadaic acid. Furthermore, constitutive expression of either Bcl-X(L) or Bcl-2 by gene transfer inhibited apoptosis triggered by okadaic acid in K562 cells. Thus, we suggest that protein phosphatases may be involved in maintaining the expression of bcl-2 family genes as part of the survival machinery of the cell.

Apoptosis↗
PubMed1997

[E-test to study small inhibitor concentrations, bacterial diversity and to identify presumptively beta-lactamases in strains of Pseudomonas aeruginosa and Acinetobacter baumannii associated with +nosocomial infections].

BACKGROUND: Pseudomonas aeruginosa and Acinetobacter baumanii are two important nosocomial agents that require permanent testing of their antimicrobial susceptibility. AIM: To use E-test to determine minimal inhibitory concentrations, estimate bacterial diversity and presumably identify B-lactamases of strains of Pseudomonas aeruginosa and Acinetobacter baumanii isolated from nosocomial infections. MATERIALS AND METHODS: Sixty eight strains of Pseudomonas aeruginosa and Acinetobacter baumanii isolated in a teaching hospital were analyzed with E-test strips to determine their minimal inhibitory concentrations for different antimicrobials. RESULTS: More than 75% of Acinetobacter baumanii were resistant to Piperacillin, Cefpirome, Cefepime, Gentamicin or Amikacin, 40% of strains were resistant to Ceftazidime, 27 and 53% of isolates had a decreased susceptibility to Meropenem and Piperacillin-tazobactam respectively. Twenty eight to 54% of Pseudomonas aeruginosa strains were resistant to Cefepime, Cefpirome, Ciprofloxacin and Gentamicin. Eighteen and 10% of strains were resistant to Meropenem and Imipenem respectively. Less than 10% of strains were resistant to Amikacin, Azireonam, Piperacillin-tazobactam or Ceftazidime. Most of beta-lactam resistance of Pseudomonas aeruginosa was associated to decreased susceptibility or resistance to Cefpirome, Cefepime or to Meropenem-Imipenem and did not match clearly with known beta-lactamase profiles. CONCLUSIONS: The knowledge of susceptibility of these bacteria responsible for nosocomial infections, will help to plan the appropriate use of antimicrobials.

Acinetobacter↗
PubMed1996

Erythropoietin can promote erythroid progenitor survival by repressing apoptosis through Bcl-XL and Bcl-2.

Erythropoietin (Epo), the hormone that is the principal regulator of red blood cell production, interacts with high-affinity receptors on the surface of erythroid progenitor cells and maintains their survival. Epo has been shown to promote cell viability by repressing apoptosis; however, the molecular mechanism involved is unclear. In the present studies we have examined whether Epo acts as a survival factor through the regulation of the bcl-2 family of apoptosis-regulatory genes. We addressed this issue in HCD-57, a murine erythroid progenitor cell line that requires Epo for proliferation and survival. When HCD-57 cells were cultured in the absence of Epo, Bcl-2 and Bcl-XL but not Bax were downregulated, and the cells underwent apoptotic cell death. HCD-57 cells infected with a retroviral vector encoding human Bcl-XL or Bcl-2 rapidly stopped proliferating but remained viable in the absence of Epo. Furthermore, endogenous levels of bcl-2 and bcl-XL were downregulated after Epo withdrawal in HCD-57 cells that remained viable through ectopic expression of human Bcl-XL, further indicating that Epo specifically maintains the expression of bcl-2 and bcl-XL. We also show that HCD-57 rescued from apoptosis by ectopic expression of Bcl-XL can undergo erythroid differentiation in the absence of Epo, demonstrating that a survival signal but not Epo itself is necessary for erythroid differentiation of HCD-57 progenitor cells. Thus, we propose a model whereby Epo functions as a survival factor by repressing apoptosis through Bcl-XL and Bcl-2 during proliferation and differentiation of erythroid progenitors.

Animals↗
PubMed1996

Apoptosis induced by erythroid differentiation of human leukemia cell lines is inhibited by Bcl-XL.

The induction of tumor cell differentiation represents an attractive strategy for the treatment of a wide range of malignancies. Differentiation of HL-60 promyelocytic leukemia cells towards neutrophils or monocytes has been shown to induce apoptotic cell death, which is inhibited by bcl-2 over-expression. However, the role of the bcl-2 gene family during erythroid differentiation of human leukemia cells remains unknown. We found that human erythroleukemia (HEL) and K562, two leukemia cell lines that undergo erythroid differentiation do not express Bcl-2, but express Bcl-XL, a related protein that functions as an inhibitor of apoptosis. Differentiation of HEL or K562 cells with inducers of erythroid differentiation (hemin, retinoic acid, or transforming growth factor-beta) was accompanied by progressive cell death and degradation of genomic DNA into oligonucleosomal fragments. The loss of cellular viability was associated with downregulation of bcl-xL mRNA and protein. In contrast, the levels of Bax, another Bcl-2 family member implicated in apoptosis remained unaltered. Constitutive expression of Bcl-XL by gene transfer inhibited apoptosis triggered by erythroid differentiation of HEL K562 cells. Yet, Bcl-XL did not alter the expression of epsilon-globin, which is induced during erythoid differentiation of HEL and K562 cells, arguing that apoptosis and differentiation can be uncoupled by Bcl-XL. These results indicate that Bcl-XL acts as an antiapoptosis protein in leukemia cells that undergo erythroid differentiation and that downregulation of bcl-x is a component of the apoptotic response that is coupled to differentiation in human leukemia cells.

Apoptosis↗
PubMed1996

Response to higher doses of interferon alfa-2b in patients with chronic hepatitis C: a randomized multicenter trial. Hepatitis Interventional Therapy Group.

To evaluate response rates to 3, 5, or 10 million units (MU) of interferon alfa-2b, given thrice weekly, and to determine whether higher doses of interferon increase the likelihood or durability of the response, a multicenter, randomized trial was performed at nine academic medical centers in the United States. Two hundred forty eight patients with chronic hepatitis C were randomized to receive 3, 5, or 10 MU of interferon alfa-2b thrice weekly for 12 weeks. Based on the alanine aminotransferase (ALT) response at treatment-week 12, the patients were rerandomized to additional therapy at the same or at increased doses for an additional 12 to 36 weeks; in the case of no response to the highest dose, the patients were discontinued from the study. Serum ALT concentrations and liver histology were measured. The overall complete response rates to 3, 5, or 10 MU were not different at treatment-week 12 (31% vs. 42% vs. 40%, not significant). The majority of week-12 responders continued to respond during additional treatment. When the treatment was discontinued, 15.4% to 19.0% of patients maintained their response. Of the nonresponders to 3 MU at week 12, who were continued on 3 MU for an additional 12 weeks, none responded. However, response to additional therapy occurred in 12% of week-12 nonresponders, whose dose was escalated from 3 or 5 MU to 10 MU. The only baseline features associated with the treatment response were the absence of fibrosis or cirrhosis on the pretreatment liver biopsy and viral genotype. We conclude that the initial response to interferon in patients with chronic hepatitis C is not increased by treatment with higher doses of the drug. Patients who do not respond to 3 MU by treatment-week 12 will not respond with continued therapy at that dose; however, a proportion of patients who do not respond to 12 weeks of treatment with 3 or 5 MU may respond to higher doses. Although the long-term sustained response rates are marginally increased with interferon doses above 3 MU three times per week, the side effects are difficult to tolerate. The analysis of baseline factors in relation to response identified no single baseline factor associated with a low-enough response rate to warrant withholding interferon therapy from patients with chronic hepatitis C.

Adolescent↗
PubMed1996

Advances in drug analysis by kinetic methods.

Automatic kinetic methods are powerful tools for drug analysis as they use modern instrumentation and computers, which are essential for shortening analysis times and enhancing the quality of routine analyses. This paper reviews novel kinetic approaches to the determination of various types of drugs in bio(pharmaceutical) materials including the following: (a) a combination of the stopped-flow (SF) technique and fluorescence polarization immunoassay for the determination of drugs of abuse and opiates in urine; (b) the joint use of the SF technique and micelle-stabilized room-temperature phosphorimetry for the determination of anti-inflammatory drugs such as naproxen; (c) the use of sensitized luminescence by energy transfer processes for the kinetic determination of antibiotics such as tetracycline using the SF technique; and (d) the use of the continuous addition of reagent technique for determining hallucinogenic alkaloids and phenothiazines by peroxyoxalate chemiluminescence reactions. Other advances in drug analysis by kinetic methods involving kinetometric approaches (e.g. Kalman filtering) and the use of micellar catalysis are also discussed.

Chemistry Techniques, Analytical↗
PubMed1996

Sciatic nerve palsy following childbirth.

Two cases are reported of sciatic nerve palsy after delivery by Caesarean section in primigravidae. One mother was slender and had an emergency Caesarean section for failure to progress with a breech presentation. Epidural analgesia during labour was extended for operative delivery. The other mother was obese, mildly hypertensive, had a large baby with a high head and was delivered by elective Caesarean section under epidural anaesthesia. She experienced severe intrapartum hypotension. Both patients suffered right sided sciatic nerve palsy. The aetiologies of obstetric palsies and those following regional block are reviewed and the importance of careful diagnosis and of avoiding peripheral nerve compression during regional block are emphasised.

Adult↗
PubMed1996

Fluoride content of infant formulae in Australia.

The prevalence of dental fluorosis in Australia and the United States of America has increased in both optimally fluoridated and non-fluoridated areas. This has been attributed to an increase in the fluoride level of food and beverages through processing with fluoridated water, inadvertent ingestion of fluoride toothpaste, and the inappropriate use of dietary supplements. A major source of fluoride in infancy is considered to be infant formula which has been implicated as a risk factor for fluorosis in a number of studies. In this study the fluoride content of the infant formulae commonly used in Australia was determined. The acid diffusible fluoride of each powdered formula was isolated by microdiffusion and measured using a fluoride ion-specific electrode. The fluoride content of milk-based formulae ranged from 0.23 to 3.71 micrograms F/g and for soy-based formulae from 1.08 to 2.86 micrograms F/g. When reconstituted, according to the manufacturer's directions, with water not containing fluoride, the formulae ranged in fluoride content from 0.031 to 0.532 ppm, with the average fluoride content 0.240 ppm. Using average infant body masses and suggested volumes of formula consumption for infants 1-12 months of age, possible fluoride ingestion per kg body mass was estimated. None of the formulae, if reconstituted using water containing up to 0.1 ppm F, should provide a daily fluoride intake above the suggested threshold for fluorosis of 0.1 mg F/kg body mass. However, if reconstituted with water containing 1.0 ppm F they should all provide a daily fluoride intake of above the suggested threshold for fluorosis with intakes up to 2-3 times the recommended upper 'optimal' limit of 0.07 mg/kg body mass. Under these conditions the water used to reconstitute the formulae would provide 65-97 percent of the fluoride ingested. These figures are likely to be overestimates due to the intake of nutrients from other sources reducing formulae consumption and also due to the lower bioavailability of fluoride from milk-based formulae. Further, it is generally believed that the maturation stage of enamel formation is the critical period for fluorosis development by chronic, above-threshold fluoride exposure. The maturation stage for the anterior permanent teeth, however, is after the first twelve months of life where fluoride intake from infant formula consumption per kg body mass is highest. The level of fluoride in the commonly used Australian formulae would suggest that infant formula consumption alone is unlikely to be a risk factor for dental fluorosis in a non-fluoridated community, but could make a major contribution to an infant's daily fluoride intake. However, prolonged consumption (beyond 12 months of age) of infant formula reconstituted with optimally-fluoridated water could result in excessive amounts of fluoride being ingested during enamel development of the anterior permanent teeth and therefore may be a risk factor for fluorosis of these teeth.

Acids↗
PubMed1996

[Delayed hypersensitivity to evoked antigens: normal values in Chilean young adults].

Delayed hypersensitivity skin test are widely accepted as in vivo measure of cellular immunity. Since genetic and environmental factors may affect these tests, each population must establish its own normal values. The aim of this work was to study delayed hypersensitivity in Chilean normal young adults. We studied the response to eight antigens using the Multitest CMI (Rhodia Merieux) in 50 students (22 females, 28 males), aged 18 to 25 years old. Skin tests were read at 24, 48 and 72 hours. At 48 Hours, 60% of women responded to 3 and 68% of men to 4 antigens. A mean response to 3.6 antigens was observed. Total score in men and women were 19.5 +/- 7.3 and 12.2 +/- 6.5 mm respectively (p < 0.05). These figures are different from those published abroad and confirm the need for national standards.

Adolescent↗
PubMed1996

An intelligent information systems architecture for clinical decision support on the Internet.

This paper presents a prototype of an agent-based intelligent information systems architecture that can provide clinical decision support in a distributed, heterogeneous environment such as the Internet. After presenting the architecture, a specific transaction sequence is detailed and implemented to test the architecture. A transaction sequence is a detailed analysis of all actions by all entities to accomplish the system goal. In this case, the goal is to give decision support information access to a provider in the context of a computerized patient record. Based on the results of the prototype implementation, we argue that the system is scaleable and discuss other transactions, standards, and needed development.

Computer Communication Networks↗
PubMed1996

[Clinical usefulness of Multitest in the evaluation of cellular immunity].

The aim of this work was to assess cellular immunity using the Multitest CMI and relate its results with lymphocyte counts and lymphocyte subpopulations determined using monoclonal antibodies against CD4 and CD8 and fluorescence microscopy. We studied 51 patients (31 male), 20 infected with HIV, 18 recurring infections, 5 with cancer, 2 with tuberculosis and 6 with miscellaneous diagnoses. According to Multitest results, patients were classified as normal, hypoergic or anergic. Twenty five percent of patients were normal, 65% hypoergic and 10% anergic. Eighty percent of anergic patients were infected with HIV. No differences in total lymphocyte count were observed between the three groups. CD4 lymphocyte count was lower in anergic patients when compared with the other two groups. All patients with CD4 counts below 200 cells/mm3 were anergic. It is concluded that Multitest CMI is useful for the assessment of cellular immunity and complements the determination of lymphocyte subpopulations.

Adult↗
PubMed1995

Multicomponent kinetic determinations using artificial neural networks.

Neural networks were successfully used for multicomponent kinetic determinations of species with rate constant ratios approaching unity without the aid of spectral discrimination. The ensuing method relies on two inputs describing the profile of the kinetic curve for each mixture, which is obtained by preprocessing kinetic data using nonlinear least-squares regression. A straightforward network architecture (2:4s:21) was used to resolve mixtures of 2- and 3-chlorophenol; the trained network estimated the concentrations of both components in the mixture with a relative standard error of prediction of approximately 5%, which is much lower than that obtained with Kalman filtering. The effect of some variables such as the rate constant and analyte concentration ratios on the proposed multicomponent determination is discussed.

Chlorophenols↗
PubMed1995

The developmental stage of inactivation of rye origin rRNA genes in the embryo and endosperm of wheat x rye F1 hybrids.

To identify the developmental stage during which the preferential inactivation of rRNA genes from the rye parent occurs in wheat x rye hybrids, nucleolar activity was evaluated in the embryo and endosperm of developing seeds of the hybrids. The hybrids were obtained from crosses of euploid and aneuploid lines of hexaploid wheat, Triticum aestivum cv. Chinese Spring, with rye, Secale cereale cv. Centeio do Alto. The number of nucleolar organizing regions (NORs) and nucleoli present in the embryo and endosperm cells of wheat, and wheat x rye F1 hybrids, at different times after fertilization was scored by silver staining. The inactivation of rDNA of rye origin in F1 hybrids occurs simultaneously in the embryo and in the endosperm between 4 and 5 days after fertilization, when these have been through six and 10 cell cycles respectively. We conclude that the genomic interactions leading to the inactivation of the rye origin rDNA is a time-dependent process, related to the developmental stage and independent of the number of cell cycles (DNA replication rounds) they have been through.

Cell Count↗
PubMed1995

Reprogramming of rye rDNA in triticale during microsporogenesis.

To test the hypothesis that interspecific genomic and chromosome interactions leading to nucleolar dominance could be reprogrammed in meiosis, we compared the expression of distinct nucleolar organizing region (NOR) loci in hexaploid triticale root tip meristematic cells, pollen mother cells and young pollen grains. Interphase and metaphase cells were silver stained to quantify nucleoli and active NOR loci respectively. A marked difference in the ribosomal RNA gene activity of each locus was observed when different types of cells were compared: in somatic and pollen mother cells, rRNA gene activity was mainly restricted to major wheat NORs (1B and 6B) with only a small contribution from rye NORs (1R). In contrast, in young pollen grains, all NORs present, including the 1R NORs, were consistently active. The expression of all NORs just after meiosis is considered to be a consequence of meiotic reprogramming of rye origin rDNA. Gene reprogramming mediated by the resetting of methylation patterns established early in embryogenesis is suggested to be responsible for the differential expression of the NORs of rye origin in distinct developmental stages of triticale.

DNA, Plant↗
PubMed1995

Low-dose, titratable interferon alfa in decompensated liver disease caused by chronic infection with hepatitis B virus.

BACKGROUND & AIMS: Interferon therapy has been associated with a number of severe side effects when administered to patients with decompensated cirrhosis caused by chronic hepatitis B. The safety and potential efficacy of a low-dose, titratable regimen of interferon alfa-2b in patients with decompensated liver disease caused by chronic hepatitis B virus infection were studied. METHODS: Twenty-six patients were treated at five medical centers. Five patients had Child's class A status, 15 had Child's B status, and 6 had Child's C status. Treatment was continued for 24 weeks whenever possible. Dose adjustments were made according to predefined safety criteria. RESULTS: All patients with Child's A status responded with a sustained loss of serum hepatitis B virus DNA, reduction in aminotransferase activity, and clinical stabilization. Only 5 patients with Child's B (33%) and no patients with Child's C status reached similar end points. The probability of survival was greater in responders than in nonresponders (P = 0.017). Three patients each developed serious infections or greater than twofold increases in serum aminotransferase levels during therapy. CONCLUSIONS: Low-dose, titratable interferon therapy is safer than previously reported regimens. Nonetheless, serious infections were observed relatively frequently, and this therapy should be reserved for individuals with mild to moderate hepatic decompensation, preferably patients with Child's A status.

Adult↗