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Biomedical subjects

A Martinez

Publications and source records attributed to A Martinez.

At least 199 records · Page 11Linked to original sources
PubMed1997

Crystallization and preliminary diffraction analysis of a truncated homodimer of human phenylalanine hydroxylase.

A recombinant truncated form (delta1-102/delta428-452) of the non-heme iron-dependent metalloenzyme human phenylalanine hydroxylase (hPAH, phenylalanine 4-monooxygenase; EC 1.14.16.1) was expressed in E. coli, purified to homogeneity as a homodimer (70 kDa) and crystallized using the hanging drop vapour diffusion method. The crystals are orthorhombic, space group C222 with cell dimensions of a = 66.6 A, b = 108.4 A, c = 125.7 A. The calculated packing parameter (Vm) is 3.24 A3/Da with four 2-fold symmetric dimers (or eight momomers) in the unit cell. Data have been collected to 2.0 A resolution.

Crystallization↗
PubMed1997

Adaptive modification of treatment planning to minimize the deleterious effects of treatment setup errors.

PURPOSE: Using daily setup variation measured from an electronic portal imaging device (EPID), radiation treatment of the individual patient can be adaptively reoptimized during the course of therapy. In this study, daily portal images were retrospectively examined to: (a) determine the number of initial days of portal imaging required to give adequate prediction of the systematic and random setup errors; and (b) explore the potential of using the prediction as feedback to reoptimize the individual treatment part-way through the treatment course. METHODS AND MATERIALS: Daily portal images of 64 cancer patients, whose treatment position was not adjusted during the course of treatment, were obtained from two independent clinics with similar setup procedures. Systematic and random setup errors for each patient were predicted using different numbers of initial portal measurements. The statistical confidence of the predictions was tested to determine the number of daily portal measurements needed to give reasonable predictions. Two treatment processes were simulated to examine the potential opportunity for setup margin reduction and dose escalation. The first process mimicked a conventional treatment. A constant margin was assigned to each treatment field to compensate for the average setup error of the patient population. A treatment dose was then prescribed with reference to a fixed normal tissue tolerance, and then fixed in the entire course of treatment. In the second process, the same treatment fields and prescribed dose were used only for the initial plan and treatment. After several initial days of treatments, the treatment field shape and position were assumed to be adaptively modified using a computer-controlled multileaf collimator (MLC) in light of the predicted systematic and random setup errors. The prescribed dose was then escalated until the same normal tissue tolerance, as determined in the first treatment process, was reached. RESULTS: The systematic setup error and the random setup error were predicted to be within +/-1 mm for the former and +/-0.5 mm for the latter at a > or = 95% confidence level using < or = 9 initial daily portal measurements. In the study, a large number of patients could be treated using a smaller field margin if the adaptive modification process were used. Simulation of the adaptive modification process for prostate treatment demonstrates that additional treatment dose could be safely applied to 64% of patients. CONCLUSION: The adaptive modification process represents a different approach for use of on-line portal images. The portal imaging information from the initial treatments is used as feedback for reoptimization of the treatment plan, rather than adjustment of the treatment setup. Results from the retrospective study show that the treatment of individual patient can be improved with the adaptive modification process.

Algorithms↗
PubMed1997

Reproducible rat model for comparing late rectal toxicity from different brachytherapy techniques.

PURPOSE: Newer brachytherapy techniques, such as pulse-simulated low dose rate (PDR) and high dose rate (HDR) offer clinical and technical advantages over the conventional continuous low dose rate (CLDR) irradiation. The impact of these techniques on late normal tissue toxicity has remained largely undefined, with mathematical modeling and limited clinical experience providing some guidelines. We sought to develop a reproducible rat model for quantifying and comparing late rectal toxicity from different brachytherapy techniques. METHODS AND MATERIALS: An intrarectal applicator has been designed and techniques have been developed to deliver clinically relevant doses of CLDR to allow comparison to PDR and HDR. Female Wistar rats are utilized. The endpoints assessed are rectal obstruction and a histological grading of late rectal injury. RESULTS: Analysis of 65 rats given either sham or single acute pulse irradiation has demonstrated the model to be reproducible and reliable in evaluating late rectal toxicity. CONCLUSIONS: The use of this rat model to compare late rectal injury from various doses, dose rates, and fractionation parameters utilized by CLDR, PDR, and HDR will provide another tool for safely implementing these techniques into the clinical setting.

Animals↗
PubMed1997

Efficacy of a vancomycin solution to prevent bacteremia associated with an indwelling central venous catheter in neutropenic and non-neutropenic cancer patients.

We evaluated the efficacy of a vancomycin solution in the prevention of bacteremia caused by vancomycin-sensitive organisms (VSO) in cancer patients with a tunneled central venous catheter (CVC). Eighty-three patients who had a single lumen CVC were randomized to use a heparin solution (25 U/ml) for daily catheter flush with (HepVan) or without (Hep) vancomycin, 25 mcg/ml. Febrile episodes were recorded, and central and peripheral blood cultures were drawn before beginning antibiotic therapy. Patients participated in follow-up to 16,677 catheter days (8,666 Hep and 8,011 HepVan), and 143 febrile episodes were recorded (82 Hep and 61 HepVan). Forty-four episodes of bacteremia occurred, 23 of them due to VSO (16 occurred in the Hep group and 7 in the HepVan group (P = 0.19). VSO bacteremia occurred in 14 neutropenic (absolute neutrophil count < 500 x 10(9)/l) episodes (7 Hep vs. 7 HepVan) and in 9 non-neutropenic episodes (9 Hep vs. O HepVan; P = 0.013). Vancomycin effectively prevented bacteremia by VSO in non-neutropenic patients, supporting the idea that intraluminal colonization of indwelling CVCs contributes to bacteremia only in these patients.

Adolescent↗
PubMed1997

E280A PS-1 mutation causes Alzheimer's disease but age of onset is not modified by ApoE alleles.

A single base substitution of a glutamic acid to an alanine codon 280 was found in the presenilin-1 (PS-1) gene on chromosome 14 in affected individuals in each of seven Colombian early-onset Alzheimer's disease (AD) kindreds. The mutation segregated with disease in kindreds tested. In the largest kindred (C2), the maximum two-point lod score between the mutation and AD was Z = 8.14 at theta = 0. The presence of a single mutation and the common geographic origin, with all families from the state of Antioquia, suggest a founder effect in this population. This finding is supported by the observation of a rare haplotype inherited with AD in all kindreds. These kindreds form the largest collection of AD cases with the same PS-1 mutation and the same educational, environmental, and ethnic background in which to study the phenotypic effect of putative risk factors, such as the epsilon4 allele of apolipoprotein E (ApoE) or head trauma. Of the few AD cases having a history of head trauma, the age of onset was not lowered. No effect of ApoE genotype on the age of onset was detected. Previous investigations of the effect of ApoE genotype on the age of onset were confounded by small patient numbers, familial clustering of ApoE genotypes, and combining data from unrelated families with different mutations.

Adult↗
PubMed1997

Association between trisomy 8 and the immunophenotype of blast cells from acute leukemias secondary to a myelodysplastic syndrome or chronic myeloproliferative disorders.

In the present study we have used FISH to analyze the incidence of trisomy 8 in acute leukemias following either a primary myeloproliferative disorder (MPD) or a myelodysplastic syndrome (MDS) and correlated it with both the immunophenotype and the cell-cycle distribution of the leukemic blast cells. Six of the 21 (28%) acute leukemias studied displayed trisomy 8 by FISH. The number of trisomic cells in these cases ranged from 20 to 84%, with a mean of 46 +/- 24%. Trisomy 8 was associated with a homogeneous population of leukemic cells, phenotypically characterized by CD34+/HLADR+/CD13+/CD33+/CD11b-/ CD15-/CD14-. No significant differences were observed on the proliferative rate of cases with trisomy 8, as compared with blast cells from the remaining patients. Overall, our findings suggest that in acute leukemias secondary to MPD or MDS, trisomy 8 is associated with a blockade of myeloid maturation at an early step of the differentiation process.

Acute Disease↗
PubMed1997

In leukemic hematopoiesis CD34 antigen does not have the same significance as it does normal hematopoiesis.

The aim of the present study was to analyze whether or not leukemic clonogenic cells are restricted to the CD34+ cell fraction and to investigate the effect of IL-3 and G-CSF on blast cell populations dissected according to their CD34 reactivity. For this purpose 34 patients were studied. Patients were classified into three groups according to CD34 antigen expression: (1) cases in which all blast cells (100%) were positive for the CD34 Ag (n = 9); (2) cases in which all blast cells lacked the expression of this antigen (n = 10); and (3) patients in whom both, CD34 positive and negative blast cell subsets coexisted (n = 15). In 15 cases immunomagnetic cell selection was performed and two subpopulations were separated: one, phenotypically more immature (CD34+), and another, theoretically more differentiated (CD34-/33+). In addition, in three cases both CD34+ and CD34- blast cell subpopulations were sorted using a FACStar flow cytometer. Blast colony assays were performed using 0.9% methylcellulose and two different recombinant human hematopoietic growth factors (HGFs), IL-3 and G-CSF, were used as growth stimulants. Either, a single or a combination of the growth factors was added to cultures. Colony formation was observed in both 100% positive or 100% negative cases for the CD34 antigen as well as in the CD34+ and CD34- cell fractions separated by immunomagnetic selection or flow cytometry. The effect of G-CSF and IL-3 on both cell fractions was as follows: cases with a uniform population according to CD34 expression (100% positive or negative) showed a better growth response with IL-3 especially for the CD34+ cases (87% vs 40% of CD34+ and CD34- cases, respectively). Within the CD34-/33+ selected fractions, IL-3 tended to induce a higher proliferative response than G-CSF while the opposite was found within the CD34+ cell selected fractions. In contrast it was observed that both IL-3 and G-CSF induced a higher PE on the CD34- blast cells (both selected and 100% negative), although the difference was not statistically significant. The existence of a possible synergistic effect (SE) between HGFs was also explored. Overall, a synergistic growth was observed in nine out of the 13 selected cases studied and this effect could be seen in both CD34- or CD34+ blast cell fractions. The analysis of the complete phenotypic characteristics of these cells revealed that cell fractions showing SE were more immature according to the expression of CD15 and HLA-DR antigens. We can conclude that in leukemic hematopoiesis, CD34 antigen expression does not have the same significance as it does in normal hematopoiesis since clonogenic cells are not restricted to the CD34+ acute myeloid leukemia (AML) blast cell fraction. Moreover, our study shows that the heterogeneous response to HGFs observed in AML patients may be associated with the existence of immunophenotypically different blast cell subsets.

Adolescent↗
PubMed1997

Herpes simplex virus encephalitis in a renal transplant patient: diagnosis by polymerase chain reaction detection of HSV DNA.

A case of herpes simplex virus (HSV) encephalitis with disseminated primary HSV infection in a renal transplant patient is described. The diagnosis of the disease was achieved by nested polymerase chain reaction (PCR)-DNA in cerebrospinal fluid (CSF). Other diagnostic measures (immunoglobulin [Ig] M and virological cultures both in blood and CSF) were negative. Blood IgG gave a false-positive signal. Although ganciclovir is not the drug of choice, its concomitant administration in our patient as a prophylactic measure against CMV infection may have decreased the usual severity normally expected in this kind of primary HSV infection. The subsequent increase in ganciclovir dose to full therapeutic range, which was implemented before the diagnosis was achieved, led to the disappearance of symptoms. The detection of PCR-DNA in CSF will probably become the diagnostic method of choice. One of its great advantages, in addition to its diagnostic reliability, is that it may obviate the performance of many cerebral biopsies.

Adult↗
PubMed1997

Molecular modeling of (E)-1-alkyl-4(3)-[2-(1H-azolyl)vinyl]-pyridinium salts and evaluation of their behavior towards choline acetyltransferase.

A new type of extended pi-system aza-analogue of (E)-4-[2-(1-naphthylvinyl)]-1-substituted pyridinium salts (NVP+) has been designed and its inhibitory activity towards choline acetyltransferase (ChAT) has been evaluated in vitro. Among the several examples of the title quaternary salts synthesized 2 and 3, the indolylvinylpyridinium salt 2e is the only one to show a very low ChAT inhibition. The molecular modeling study is highly illustrative of their behavior towards ChAT and interaction with the recognition site. Thus, several selected cations together with the reference NVP+ compound 1a were studied at the PM3 and AM1 levels respectively. At the global minima, all the compounds are planar, which, from the electron charge distribution, shows a degree of polarization similar to the NVP+ model compound 1a. However, the fitting of all optimized structures indicated that only the indole derivative 2e showed the same aromatic fragment orientation as 1a, which allows us to define a volume that is not accessible to ligands in the enzyme and consequently to a refined model of the choline acetyltransferase recognition site.

Animals↗
PubMed1997

Evaluation of the AVOXimeter: precision, long-term stability, linearity, and use without heparin.

OBJECTIVES: Because the AVOXimeter uses disposable cuvettes and makes its measurements directly in whole blood without first hemolyzing the sample, it does not need the care and maintenance that conventional co-oximeters require, it operates faster than conventional co-oximeters, and it is less expensive. Therefore, the objectives of the study were (1) to evaluate the precision and linearity of the AVOXimeter's measurements of total hemoglobin concentration and oxyhemoglobin saturation; (2) to assess its long-term stability and thus the required interval for recalibration; (3) to determine whether measurements can be made without anticoagulants; and (4) to assess the feasibility of storing blood samples in the disposable cuvettes. METHODS: Measurements made by the test instrument were compared with those of conventional co-oximeters or with standardized hemoglobin solutions. Blood samples were also collected with and without heparin to determine whether anticoagulation is necessary. RESULTS: Our tests confirmed the specified precision of 0.3 g/dl for total hemoglobin and 0.5% for oxyhemoglobin. The results also showed that these measurements were linear when compared with a conventional co-oximeter, and they were consistent with the specified accuracy of 0.45 g/dl for total hemoglobin and 1% for oxyhemoglobin. Weekly checks with control solutions showed that the instrument holds its calibration for a year or more. Although treating syringes with heparin caused dilution errors, heparin did not affect the measurements when dilution was avoided. When blood samples were placed in disposable cuvettes and read repeatedly at 1-min intervals for 20 min, the readings drifted appreciably away from the original value. This drift occurred so slowly that readings taken at the first and second minute after the cuvette was filled were within 1 or 2% of the original reading. CONCLUSIONS: In our experience the test instrument was simple and easy to operate. It met the specification for precision and accuracy, its measurements were highly linear, and it maintained a stable calibration for one year. If the cuvettes are filled as soon as blood is drawn, anticoagulation is unnecessary. However, the cuvettes should be read with 1 min of filling the cuvette.

Blood Specimen Collection↗
PubMed1997

An auxiliary peptide required for the function of two activation domains in upstream stimulatory factor 2 (USF2) transcription factor.

Ubiquitous upstream stimulatory factors (USF1, USF2a and USF2b) are members of the basic-helix-loop-helix-leucine-zipper family of transcription factors that have been shown to be involved in the transcriptional response of the L-type pyruvate kinase (L-PK) gene to glucose. To understand the mechanisms of action of the USF2 isoforms, we initiated a series of co-transfection assays with deletion mutants and Ga14-USF2 fusions. The transactivating efficiency of the different native and mutant factors was determined at similar DNA binding activity. We found that: (i) exons 3- and 5-encoded regions are activation domains, (ii) a modulator domain encoded by exon 4 could be necessary to their additive action, (iii) a hexapeptide encoded by the first 5' codons of exon 6 is indispensable for transmitting activation due to both exon 3- and exon 5-encoded domains to the transcriptional machinery. Therefore, USF2 presents a modular structure and mediates transcriptional activation thanks to two non-autonomous activation domains dependent on an auxiliary peptide for expressing their activating potential.

Base Sequence↗
PubMed1997

Adaptive radiation therapy.

Adaptive radiation therapy is a closed-loop radiation treatment process where the treatment plan can be modified using a systematic feedback of measurements. Adaptive radiation therapy intends to improve radiation treatment by systematically monitoring treatment variations and incorporating them to re-optimize the treatment plan early on during the course of treatment. In this process, field margin and treatment dose can be routinely customized to each individual patient to achieve a safe dose escalation.

Confidence Intervals↗
PubMed1997

Occupational allergy in saffron workers.

Sensitization to the flower of saffron, a plant commonly grown in Spain for commercial purposes, and its clinical significance as an occupational allergen were studied. The prick test and RAST, with saffron pollen, stamen, and pistil extracts, were used to evaluate the cutaneous and specific antibody responses in the studied population. Provocation tests in patients with clinical findings were used to verify the implication of saffron components in these symptoms. Fifty saffron workers were evaluated. Three of them were sensitized to saffron pollen and stamen proteins, giving prick and RAST positive values. One patient presented asthma, showing a positive bronchial provocation test, and two patients rhinoconjunctivitis, showing positive conjunctival provocation tests. Of a general allergic population of 237, 10 patients also presented cutaneous test and IgE positive to saffron. Saffron allergens (from pollen and stamens) were characterized by SDS-PAGE immunoblotting. A relevant allergen of 15.5 kDa with profilinic nature was detected and further purified by high-resolution gel filtration chromatography. No allergenic components were demonstrated in pistils. Cross-reactivity of saffron extracts was evaluated by RAST inhibition with respect to other pollen species commonly causing sensitization in the same area of study. A significant degree of cross-reactivity was demonstrated between saffron and Lolium, Salsola, or Olea. The identification of the protein components involved in the cross-reactions was investigated by blot inhibition.

Adolescent↗
PubMed1997

Protection of DNA during oxidative stress by the nonspecific DNA-binding protein Dps.

Reactive oxygen species can damage most cellular components, but DNA appears to be the most sensitive target of these agents. Here we present the first evidence of DNA protection against the toxic and mutagenic effects of oxidative damage in metabolically active cells: direct protection of DNA by Dps, an inducible nonspecific DNA-binding protein from Escherichia coli. We demonstrate that in a recA-deficient strain, expression of Dps from an inducible promoter prior to hydrogen peroxide challenge increases survival and reduces the number of chromosomal single-strand breaks. dps mutants exhibit increased levels of the G x C-->T x A mutations characteristic of oxidative damage after treatment with hydrogen peroxide. In addition, expression of Dps from the inducible plasmid reduces the frequency of spontaneous G x C-->T x A and A x T-->T x A mutations and can partially suppress the mutator phenotype of mutM (fpg) and mutY alleles. In a purified in vitro system, Dps reduces the number of DNA single-strand breaks and Fpg-sensitive sites introduced by hydrogen peroxide treatment, indicating that the protection observed in vivo is a direct effect of DNA binding by Dps. The widespread conservation of Dps homologs among prokaryotes suggests that this may be a general strategy for coping with oxidative stress.

Bacterial Proteins↗
PubMed1997

Occupational allergic disease in cereal workers by stored grain pests.

It is well known that workers occupationally exposed to grain dust have a high prevalence of respiratory symptoms, but their pathogenesis remains obscure when sensitization to cereal flour cannot be demonstrated. Storage mites, tenebroids, and cockroaches are stored-grain pests found in grain and cereal products frequently in our area, where the cereal industry is the most important industry. An epidemiological analysis of sensitization of these stored-grain pests was performed on 4379 patients residing in an area of cereal industries. Fifty grain workers were selected for in vivo diagnostic tests with nine genera of mites, Tenebrio molitor and Blatta orientalis. Specific IgE antibodies to the extracts were demonstrated by prick tests and RAST. Association between respiratory symptoms and occupational exposure was confirmed by challenge tests (specific and methacholine). The prevalence of mite sensitization in the total sample studied (4379) was 18.96% (SEM 0.58, 95% CI 16.93-19.19). The prevalence of sensitization to storage mites among mite-sensitive patients was 11.88% (SEM 1.15, 95% CI 9.63-14.3). Among the 50 selected patients the most frequent sensitization was that to Dermatophagoides pteronyssinus (58%), followed by Dermatophagoides frinae (48%), Lepidoglyphus destructor and Tyrophagus putrescentiae (38%), Blomia kulagini (34%), and Acarus siro and Chortoglyphus arcuatus (24%). In addition, 22% of the patients presented negative prick tests and RAST for Dermatophagoides species with positive test to storage mites. Fifty percent of the 50 patients were sensitizated to Tenebrio molitor (SEM 0.7, CI 95% 36-64), and 36% to Blatta orientalis (SEM 0.67, CI 95% 23-49). The identification of mites, tenebroids, and cockroaches in dust samples yields useful data for the diagnosis of our patients.

Adolescent↗