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C Colominas

Publications and source records attributed to C Colominas.

7 recordsLinked to original sources
PubMed2004

Assessment of a technique for 2D-3D registration of cerebral intra-arterial angiography.

This study assesses the ability of a computer algorithm to perform automated 2D-3D registrations of digitally subtracted cerebral angiograms. The technique was tested on clinical studies of five patients with intracranial aneurysms. The automated procedure was compared against a gold standard manual registration, and achieved a mean registration accuracy of 1.3 mm (SD 0.6 mm). Two registration strategies were tested using coarse (128 x 128 pixel) or fine (256 x 256 pixel) images. The mean registration errors proved similar but registration of the lower resolution images was 3 times quicker (mean registration times 33 s, SD 13 s for low and 150 s SD 48 s for high resolution images). The automated techniques were considerably faster than manual registrations but achieved similar accuracy. The technique has several potential uses but is particularly applicable to endovascular treatment techniques.

Algorithms↗
PubMed2001

Synthesis and biological activity of 7-oxo substituted analogues of 5-deaza-5,6,7,8-tetrahydrofolic acid (5-DATHF) and 5,10-dideaza-5,6,7,8-tetrahydrofolic acid (DDATHF).

We recently described the syntheses of 12a-c, 4-amino-7-oxo substituted analogues of 5-deaza-5,6,7,8-tetrahydrofolic acid (5-DATHF), and 5,10-dideaza-5,6,7,8-tetrahydrofolic acid (DDATHF), in six steps from commercially available p-substituted methyl benzoates in 20-27% overall yields. Such analogues were tested in vitro against CCRF-CEM leukemia cells and showed that they are completely devoid of any activity, the IC(50) being higher than 20 microg/mL for all cases. To clarify if the presence of the carbonyl group in position C7, the distinctive feature of our synthetic methodology, is the reason for this lack of activity, we have now obtained the 7-oxo substituted analogues of 5-DATHF and DDATHF, 18a-c, in 10-30% overall yield. Testing of 18a-c in vitro against CCRF-CEM leukemia cells revealed that these compounds are totally inactive. A molecular modeling study of 18b inside the active site of the complex E. coliGARTFase-5-DATHF-GAR pointed to an electronic repulsion between the atoms of the 7-oxo group and the carbonyl group of Arg90 as a possible explanation for the inactivity of 18a-c.

Antineoplastic Agents↗
PubMed2001

Selective hydrolysis of 2,4-diaminopyrimidine systems: a theoretical and experimental insight into an old rule.

Hydrolysis of the amino groups in condensed 2,4-diaminopyrimidine systems (1) has been used as a common method for the synthesis of oxo-substituted pyrimidines. In particular, the treatment with 6 M HCl usually yields exclusively the 2-amino-4-oxopyrimidine isomer (2). During our work, we found that the hydrolysis of the amino groups present in some condensed 2,4-diaminopyrimidine systems unexpectedly afforded exclusively the 4-amino-2-oxopyrimidine isomer (3). In this paper, we present the experimental work and ab initio calculations carried out to understand this discrepancy. As a part of such study, eight compounds containing a 2,4-diaminopyrimidine moiety were calculated in gas phase and in aqueous solution, and some acid hydrolyses were reexamined. Results showed that the presence of an electron-donating nitrogen linked to C6 of the 2,4-diaminopyrimidine ring changes the preferred hydrolysis site to yield the 4-amino-2-oxopyrimidine isomer.

Chemical Phenomena↗
PubMed2001

A high-performance liquid chromatography based strategy for rapid, sensitive sequencing of N-linked oligosaccharide modifications to proteins in sodium dodecyl sulphate polyacrylamide electrophoresis gel bands.

The majority of biologically active proteins are glycosylated, therefore any approach to proteomics which fails to address the analysis of oligosaccharides is necessarily incomplete. To appreciate the structure of a glycoprotein fully, to understand the roles for the attached oligosaccharides and to monitor disease associated changes it is necessary to visualise the sugars as well as the protein. To achieve this aim when biological samples are available at the low microgram level or less has involved increasing the sensitivity of the technology for glycan analysis. Since one protein may have many different oligosaccharides attached to it (glycoforms) this is a major technical challenge. CD59, for example, has over 100 different sugars at one N-linked glycosylation site. Applications of recently developed technology suggest that it is now becoming realistic to extend the proteomics analysis of glycoproteins to include details of glycosylation. This is achieved by releasing the N-glycans from the protein in a gel by optimised peptide-N-glycosidase F digestion. The released glycans are then tagged with the fluorophore, 2-amino benzamide. The labelled glycan pools (containing 50-100 femtomoles of glycans) are resolved by predictive normal phase high performance liquid chromatography (HPLC) on an amide based column or by reverse phase HPLC on a C18 column. Preliminary structural assignments are confirmed by exoglycosidase array digestions of the entire glycan pool. Complementary matrix-assisted laser desorption/ionization-mass spectrometry, which requires 10-20 times as much sugar for a single run, can be used where there is sufficient material. This provides a composition analysis but not linkage information.

Amidohydrolases↗
PubMed1999

Cell-specific glycoforms of sialoadhesin and CD45 are counter-receptors for the cysteine-rich domain of the mannose receptor.

We previously reported that CR-Fc, an Fc chimeric protein containing the cysteine-rich (CR) domain of the mannose receptor, binds to marginal zone metallophilic macrophages (Mo) and B cell areas in the spleen and to subcapsular sinus Mo in lymph nodes of naive mice (CR-Fc(+) cells). Several CR-Fc ligands were found in spleen and lymph node tissue lysates using ligand blots. In this paper we report the identification of two of these ligands as sialoadhesin (Sn), an Mo-specific membrane molecule, and the leukocyte common antigen, CD45. CR-Fc bound selectively to Sn purified from spleen and lymph nodes and to two low molecular weight isoforms of CD45 in a sugar-dependent manner. CR-Fc binding and non-binding forms of Sn, probably derived from CR-Fc(+) and CR-Fc(-) cells respectively, were selected from spleen lysates. Analysis of the glycan pool associated with the CR-Fc-binding form revealed the presence of charged structures resistant to sialidase, absent in the non-binding form, that could correspond to sulfated structures. These results confirm the identification of the CR region of the mannose receptor as a lectin. We also demonstrate that the same glycoprotein expressed in different cells of the same organ can display distinct sugar epitopes that determine its binding properties.

Animals↗
PubMed1999

Glycosylation differences between the normal and pathogenic prion protein isoforms.

Prion protein consists of an ensemble of glycosylated variants or glycoforms. The enzymes that direct oligosaccharide processing, and hence control the glycan profile for any given glycoprotein, are often exquisitely sensitive to other events taking place within the cell in which the glycoprotein is expressed. Alterations in the populations of sugars attached to proteins can reflect changes caused, for example, by developmental processes or by disease. Here we report that normal (PrP(C)) and pathogenic (PrP(Sc)) prion proteins (PrP) from Syrian hamsters contain the same set of at least 52 bi-, tri-, and tetraantennary N-linked oligosaccharides, although the relative proportions of individual glycans differ. This conservation of structure suggests that the conversion of PrP(C) into PrP(Sc) is not confined to a subset of PrPs that contain specific sugars. Compared with PrP(C), PrP(Sc) contains decreased levels of glycans with bisecting GlcNAc residues and increased levels of tri- and tetraantennary sugars. This change is consistent with a decrease in the activity of N-acetylglucosaminyltransferase III (GnTIII) toward PrP(C) in cells where PrP(Sc) is formed and argues that, in at least some cells forming PrP(Sc), the glycosylation machinery has been perturbed. The reduction in GnTIII activity is intriguing both with respect to the pathogenesis of the prion disease and the replication pathway for prions.

Animals↗