Biomedical subjects

J Urban

Publications and source records attributed to J Urban.

At least 19 recordsLinked to original sources

PubMed2005

Silver clusters on silver sulfide nanocrystals: synthesis and behavior after electron beam irradiation.

Nanocomposite crystals, (Ag)(x)(Ag(2)S)(y) with x < y, are synthesized in micellar media. The generation of Ag clusters on Ag(2)S nanocrystals is attributed to the reduction of mobile Ag(+) ions in the Ag(2)S nanocrystals by sulfur derivatives. The proportions in the composite material can be modulated by electron beam irradiation. Using dodecanethiol as surface passivating agent, 2D self-organizations of these nanocomposite crystals are produced.

Electrons↗

PubMed2005

Ionization energies of argon clusters: a combined experimental and theoretical study.

We have measured appearance energies of Ar(n)+, n<or=30, by electron impact of gas phase clusters. Quantum-chemical calculations have been performed to determine the adiabatic and vertical ionization energies of argon clusters up to n=4 and 6, respectively. The experimental appearance energy of the dimer ion approaches, under suitable cluster source conditions, the adiabatic ionization energy. The agreement with values obtained by photoionization and threshold photoelectron-photoion coincidence (TPEPICO) spectra demonstrates that autoionizing Rydberg states are accessible by electron impact. Appearance energies of larger clusters, though, exceed the TPEPICO values by about 0.5 eV.

Journal Article↗

PubMed2004

Anisotropic copper nanocrystals synthesized in a supersaturated medium: nanocrystal growth.

In the chemical reduction of copper ions in mixed reverse micelles it is found that a large excess of reducing agent favors the production of a new generation of copper nanocrystals. At low reducing agent concentration, nanocrystals are mostly spherical, while in the supersaturated regime, they have various shapes such as pentagons, squares, triangles, and elongated forms. The nanocrystal structures, characterized by high-resolution transmission electron microscopy, are based on the face-centered cubic structure. A tentative explanation for the growth mechanism of copper nanocrystals having various shapes is proposed.

Journal Article↗

PubMed2004

Structural and optical investigations of SiO2-CdS core-shell particles.

Cadmium sulfide nanoparticles (approximately 5 nm), chemically capped using thioglycerol molecules, have been anchored onto silica particles (approximately 80 nm) functionalized with 3-aminopropyltrimethoxysilane. Transmission electron microscopy clearly showed that at a low concentration of cadmium sulfide, nanoparticles were discretely and more or less uniformly attached onto the silica particles. At a high concentration of cadmium sulfide nanoparticles, an approximately 6-nm-thick compact shell of cadmium sulfide was formed on the silica particles. In both cases the nanocrystalline nature of cadmium sulfide particles was preserved, as is evident from X-ray diffraction and optical absorption spectra.

Journal Article↗

PubMed2003

Assessment of fetal distress based on magnetic resonance examinations: preliminary report.

RATIONALE AND OBJECTIVES: Hypoxia is the main cause of injuries and intrauterine death of the fetus. Therefore, the main aim of monitoring and assessment of the fetus should be diagnosis of fetal distress before irreversible changes occur. Besides the fetal condition assessment methods used so far, in recent years in obstetrics new non-invasive imaging methods were introduced such as magnetic resonance (MR). This method enables morphologic evaluation of brain and brain tissue metabolism using magnetic resonance spectroscopy (MRS). MATERIALS AND METHODS: Twenty pregnant women with pregnancy-induced hypertension (11 cases, including 3 with coexisting diabetes mellitus and 2 with intrauterine growth retardation), chronic hypertension (2 cases), gestational diabetes mellitus (6 cases), and suspected intrauterine fetal growth retardation (IUGR) participated in the study. Cardiotocography (CTG) and Doppler ultrasound examination of the blood flow in the umbilical artery and in the middle cerebral artery were performed. RESULTS: In case of abnormal CTG and Doppler study records that indicated fetal hypoxia, MR studies showed the existence of ischemic focus in 5 patients and abnormal spectral images in 6 patients. CONCLUSION: The results of the preliminary study suggests that the use of MR in prenatal diagnosis may revolutionize the early detection of fetal injury in fetal distress. It is a valuable component of the diagnostic process, supplementing other examinations. The use of MR to assess fetal condition gives additional information and helps to make decisions about therapeutic actions.

Adult↗

PubMed2002

Formation of Cu and Cu2O nanoparticles by variation of the surface ligand: preparation, structure, and insulating-to-metallic transition.

Copper and copper (I) oxide nanoparticles protected by self-assembled monolayers of thiol, carboxyl, and amine functionalities [X(CH(2))(n)-CH(3), where X can be -COOH, -NH(2), or -SH] have been prepared by the controlled reduction of aqueous copper salts using Brust synthesis. The optical absorption spectrum (lambda(max)=289 nm) is found to be invariant with the nature of the capping molecule while the particle shape and distribution are found to depend strongly on it. A comparison of the protection efficiency for different capping agents such as dodecanethiol (DDT), tridecylamine (TDA), and lauric acid (LA) suggests that although zerovalent Cu is initially formed for dodecanethiol, all other cases allow oxidation to Cu(2)O nanoparticles. Despite the variation in particle size and relative stability, nanoparticles have been found to form oxides after a few days, especially for the case of LA and TDA surface capping. For all the samples studied, the size has been found to be 4-8 nm by high-resolution transmission electron microscopy. The protective ability is found to be better for dodecanethiol SAM (similar to the case of Au and Ag nanoparticles), while the order of capping efficiency varies as Cu-DDT>Cu-TDA>Cu-LA. In the present study we also demonstrate a reversible metal-insulator transition (MIT) in capped nanoparticles of Cu using temperature-dependent electrical resistivity measurement. However, the LA-capped sample does not show any such transition, possibly due to the oxide formation.

Journal Article↗

PubMed2002

Microbial synthesis of semiconductor CdS nanoparticles, their characterization, and their use in the fabrication of an ideal diode.

Cadmium sulfide nanoparticles were synthesized intracellularly by a Schizosaccharomyces pombe strain when challenged with 1 mM cadmium in solution. The nanoparticles, a known semiconducting material, exhibited an absorbance maximum at 305 nm. X-ray scattering data showed that the nanoparticles had a Wurtzite (Cd(16)S(20))-type hexagonal lattice structure and most of the nanoparicles were in the size range of 1-1.5 nm. The nanoparticles were used in the fabrication of a heterojunction with poly (p-phenylenevinylene). The diode exhibited approximately 75 mA/cm(2) current at 10 V when forward biased and the breakdown occurred at approximately 15 V in the reverse biased mode. These characteristics are considered ideal for a diode.

Cadmium Compounds↗

PubMed2001

Sec61p-independent degradation of the tail-anchored ER membrane protein Ubc6p.

Tail-anchored proteins are distinct from other membrane proteins as they are thought to insert into the endoplasmic reticulum (ER) membrane independently of Sec61p translocation pores. These pores not only mediate import but are also assumed to catalyze export of proteins in a process called ER-associated protein degradation (ERAD). In order to examine the Sec61p dependence of the export of tail-anchored proteins, we analyzed the degradation pathway of a tail-anchored ER membrane protein, the ubiquitin-conjugating enzyme 6 (Ubc6p). In contrast to other ubiquitin conjugating enzymes (Ubcs), Ubc6p is naturally short-lived. Its proteolysis is mediated specifically by the unique Ubc6p tail region. Degradation further requires the activity of Cue1p-assembled Ubc7p, and its own catalytic site cysteine. However, it occurs independently of the other ERAD components Ubc1p, Hrd1p/Der3p, Hrd3p and Der1p. In contrast to other natural ERAD substrates, proteasomal mutants accumulate a membrane-bound degradation intermediate of Ubc6p. Most interestingly, mutations in SEC61 do not reduce the turnover of full-length Ubc6p nor cause a detectable accumulation of degradation intermediates. These data are in accordance with a model in which tail-anchored proteins can be extracted from membranes independently of Sec61p.

Carrier Proteins↗

PubMed2001

Stage-specific inductive signals in the Drosophila neuroectoderm control the temporal sequence of neuroblast specification.

One of the initial steps of neurogenesis in the Drosophila embryo is the delamination of a stereotype set of neural progenitor cells (neuroblasts) from the neuroectoderm. The time window of neuroblast segregation has been divided into five successive waves (S1-S5) in which subsets of neuroblasts with specific identities are formed. To test when identity specification of the various neuroblasts takes place and whether extrinsic signals are involved, we have performed heterochronic transplantation experiments. Single neuroectodermal cells from stage 10 donor embryos (after S2) were transplanted into the neuroectoderm of host embryos at stage 7 (before S1) and vice versa. The fate of these cells was uncovered by their lineages at stage 16/17. Transplanted cells adjusted their fate to the new temporal situation. Late neuroectodermal cells were able to take over the fate of early (S1/S2) neuroblasts. The early neuroectodermal cells preferentially generated late (S4/S5) neuroblasts, despite their reduced time of exposure to the neuroectoderm. Furthermore, neuroblast fates are independent from divisions of neuroectodermal progenitor cells. We conclude from these experiments that neuroblast specification occurs sequentially under the control of non-cell-autonomous and stage-specific inductive signals that act in the neuroectoderm.

Animals↗

PubMed2001

Successive specification of Drosophila neuroblasts NB 6-4 and NB 7-3 depends on interaction of the segment polarity genes wingless, gooseberry and naked cuticle.

The Drosophila central nervous system derives from neural precursor cells, the neuroblasts (NBs), which are born from the neuroectoderm by the process of delamination. Each NB has a unique identity, which is revealed by the production of a characteristic cell lineage and a specific set of molecular markers it expresses. These NBs delaminate at different but reproducible time points during neurogenesis (S1-S5) and it has been shown for early delaminating NBs (S1/S2) that their identities depend on positional information conferred by segment polarity genes and dorsoventral patterning genes. We have studied mechanisms leading to the fate specification of a set of late delaminating neuroblasts, NB 6-4 and NB 7-3, both of which arise from the engrailed (en) expression domain, with NB 6-4 delaminating first. In contrast to former reports, we did not find any evidence for a direct role of hedgehog in the process of NB 7-3 specification. Instead, we present evidence to show that the interplay of the segmentation genes naked cuticle (nkd) and gooseberry (gsb), both of which are targets of wingless (wg) activity, leads to differential commitment to NB 6-4 and NB 7-3 cell fate. In the absence of either nkd or gsb, one NB fate is replaced by the other. However, the temporal sequence of delamination is maintained, suggesting that formation and specification of these two NBs are under independent control.

Animals↗

PubMed2001

Spalt modifies EGFR-mediated induction of chordotonal precursors in the embryonic PNS of Drosophila promoting the development of oenocytes.

Genes of the spalt family encode nuclear zinc finger proteins. In Drosophila melanogaster, they are necessary for the establishment of head/trunk identity, correct tracheal migration and patterning of the wing imaginal disc. Spalt proteins display a predominant pattern of expression in the nervous system, not only in Drosophila but also in species of fish, mouse, frog and human, suggesting an evolutionarily conserved role for these proteins in nervous system development. Here we show that Spalt works as a cell fate switch between two EGFR-induced cell types, the oenocytes and the precursors of the pentascolopodial organ in the embryonic peripheral nervous system. We show that removal of spalt increases the number of scolopodia, as a result of extra secondary recruitment of precursor cells at the expense of the oenocytes. In addition, the absence of spalt causes defects in the normal migration of the pentascolopodial organ. The dual function of spalt in the development of this organ, recruitment of precursors and migration, is reminiscent of its role in tracheal formation and of the role of a spalt homologue, sem-4, in the Caenorhabditis elegans nervous system.

Animals↗

PubMed2001

[Prenatal and neonatal diagnosis of osteogenesis imperfecta in obstetrical practice].

Osteogenesis imperfecta (OI types I, II, III, IV) is a heterogeneous group of genetically disorders of connective tissue. Quantitative or qualitative abnormalities of type I collagen form pathogenetical basis of the disease. They are caused by mutations in genes encoding collagen proteins or enzymes involved in collagen biosynthesis. The clinical features of each type usually correspond to the type of mutation. Typical manifestations are fragile bones with multiple bone fractures and bone deformities. Currently applied diagnosis in utero of OI II and sometimes OI III may be performed. Diagnosis of other OI phenotypes cannot be made until after birth. We present three cases of OI II (four children) diagnosed, in utero, by ultrasound examination. The analysis in work include: 1. the prenatal sonographic features of OI type II 2. the biochemical properties of collagen in the above cases 3. genetic counselling of the families affected by OI.

Fatal Outcome↗

PubMed2001

[Vanadium: threat and hope].

Vanadium is an element classified in the group of heavy metals, very common in the natural environment and widely used in industry. It is mainly used in the production of nonferrous alloys, most resistant carbon steel, as well as in chemical, glass, paint and varnish, ceramic, and photographic industries. In the atmosphere, two second of vanadium originates from anthropogenic sources, sea-born aerosols and volcanic eruptions. Municipal waste is the major source of vanadium in surface water. It is one of the components of live organisms and participates in many biochemical processes essential for their proper functioning, but in higher concentrations it may induce acute or chronic intoxication that damage biological structures and disorder biochemical systems. The mechanism of vanadium toxic effect has not as yet been elucidated, however, it is already known that this mechanism is rooted among others in vanadium properties able to hinder a number of enzymatic systems. For vanadium the most "critical" systems are respiratory, urinary and hemopoietic. Vanadium salts may also be genotoxic and harmful at different phases of reproduction and development. Numerous studies of a possible use of vanadium in treatment of certain diseases, e.g., diabetes, have been carried out. Some findings on a potential antineoplastic or contraceptive effect of vanadium compounds have recently been reported. To sum up, there are numerous hazards associated with the wide industrial use of vanadium, nevertheless, the number of findings highlighting its nutritive and therapeutic properties is growing.

Antineoplastic Agents↗

PubMed2000

IL-13-mediated worm expulsion is B7 independent and IFN-gamma sensitive.

B7 costimulation is a required component of many type 2 immune responses, including allergy and protective immunity to many nematode parasites. This response includes elevations in Th2 cytokines and associated effector functions including elevations in serum IgG1 and IgE and parasite expulsion. In studies of mice infected with Trichuris muris, blocking B7 ligand interactions inhibited protective immunity, suppressed IL-4 production, and enhanced IFN-gamma production, but unexpectedly did not inhibit production of the Th2 cytokine, IL-13. Blocking both IFN-gamma and B7 restored protective immunity, which was IL-13 dependent, but did not restore IL-4 or associated IgE responses. Although IL-13 was required for worm expulsion in mice in which both IFN-gamma and B7 were blocked, IL-4 could mediate expulsion in the absence of both IL-13 and IFN-gamma. These studies demonstrate that 1) B7 costimulation is required to induce IL-4, but not IL-13 responses; 2) IL-13 is elevated in association with the IFN-gamma response that occurs following inhibition of B7 interactions, but can only mediate IL-4-independent protection when IFN-gamma is also inhibited; and 3) increased IL-13 production, in the absence of increased IL-4 production, is not associated with an IgE response, even in the absence of IFN-gamma.

Abatacept↗

PubMed2000

Molecular identification of metastatic cancer to the skin using laser capture microdissection: a case report.

BACKGROUND: In the current study the authors report a 57-year-old woman with a scalp tumor and cervical lymphadenopathy who had a previously resected duodenal carcinoid. Histologic and immunophenotypic characteristics of the duodenal carcinoid differed from those of the scalp and cervical lymph node tumors, prompting the use of molecular methodologies to make the diagnosis. METHODS: Paraffin embedded tissues from the duodenal carcinoid, scalp, and lymph node tumors were dissected using microscopic visualization and laser capture microdissection. DNA was extracted and polymerase chain reaction (PCR) was performed to evaluate loss of heterozygosity and microsatellite alterations using primers flanking 22 polymorphic microsatellite markers from 9 chromosomal regions, including genes associated with MEN-1 (11q), CDKN2 (9p), p53 (17p), and bronchial carcinoid (3p). Microdissected lymphocytes from the three tissues were used as source of constitutional DNA (controls). RESULTS: Fourteen of the 22 markers were informative (heterozygous in control lymphocytes). A marker on 3p12 showed loss of the same parental allele in the three tumors. A different marker on 3p14.2 showed an identical shifted band in the three tumors indicative of a common microsatellite alteration. CONCLUSIONS: The shared molecular abnormalities among the three tumors indicated a common clonal origin, leading to a diagnosis of primary duodenal carcinoid with clear cell metastases to the scalp and cervical lymph nodes. These findings led to radiation therapy and immunotherapy rather than chemotherapy. This case illustrates the novel application of laser capture microdissection combined with PCR-based analyses of genomic markers for the identification of the origin of metastatic disease.

Alleles↗

PubMed2000

A regulatory link between ER-associated protein degradation and the unfolded-protein response.

Ubiquitin conjugation during endoplasmic-reticulum-associated degradation (ERAD) depends on the activity of Ubc7. Here we show that Ubc1 acts as a further ubiquitin-conjugating enzyme in this pathway. Absence of both enzymes results in marked stabilization of an ERAD substrate and induction of the unfolded-protein response (UPR). Furthermore, basic ERAD activity is sufficient to eliminate unfolded proteins under normal conditions. However, when stress is applied, the UPR is required to increase ERAD activity. We thus demonstrate, for the first time, a regulatory loop between ERAD and the UPR, which is essential for normal growth of yeast cells.

Carboxypeptidases↗

PubMed2000

[The Doppler cerebroplacental ratios and perinatal outcome in post-term pregnancy].

Our purpose was to determine whether the Doppler cerebroplacental ratios predicts perinatal outcome in postterm pregnancy. The middle cerebral to umbilical artery resistant and pulsatility indices (MCA PI/UA PI and MCA RI/UA RI) were measured in 59 postterm pregnancies. We found significant correlation between MCA PI/UA PI, MCA RI/UA RI, nonstress testing and intrapartum fetal heart rate assessment. There was also an association between MCA PI/UA PI and 1- and 5-minute Apgar score. We conclude that the Doppler cerebroplacental ratios provide useful information about perinatal outcome.

Brain↗

PubMed2000

[Cesarean section for the second twin].

Twin pregnancies delivered after 26 weeks gestation were reviewed. Of 167 twin pregnancies 101 (60.5%) were delivered by cesarean section. There were 8 combined vaginal-abdominal deliveries, including 4.8% of all twins delivered and 7.3% of all twins delivered by cesarean section. The commonest indication for the cesarean birth of the second twin was transverse lie. The data suggest that cesarean section of the second twin is not possible to predict by obstetrics variables including antepartum ultrasound. In order to decrease the rate of combined vaginal-abdominal deliveries the need to reassess the currently protocol of management for twin delivery is indicated.

Cesarean Section↗