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D Ivanov

Publications and source records attributed to D Ivanov.

At least 19 recordsLinked to original sources
PubMed2006

The Third International Intercomparison on EPR Tooth Dosimetry: part 2, final analysis.

The objective of the Third International Intercomparison on EPR Tooth Dosimetry was to evaluate laboratories performing tooth enamel dosimetry <300 mGy. Final analysis of results included a correlation analysis between features of laboratory dose reconstruction protocols and dosimetry performance. Applicability of electron paramagnetic resonance (EPR) tooth dosimetry at low dose was shown at two applied dose levels of 79 and 176 mGy. Most (9 of 12) laboratories reported the dose to be within 50 mGy of the delivered dose of 79 mGy, and 10 of 12 laboratories reported the dose to be within 100 mGy of the delivered dose of 176 mGy. At the high-dose tested (704 mGy) agreement within 25% of the delivered dose was found in 10 laboratories. Features of EPR dose reconstruction protocols that affect dosimetry performance were found to be magnetic field modulation amplitude in EPR spectrum recording, EPR signal model in spectrum deconvolution and duration of latency period for tooth enamel samples after preparation.

Electron Spin Resonance Spectroscopy↗
PubMed2006

Comparison of EPR occupational lifetime external dose assessments for Mayak nuclear workers and film badge dose data.

The Mayak worker cohort is one of the major sources of information on health risks due to protracted exposures to plutonium and external ionizing radiation. Electron paramagnetic resonance (EPR) measurements in tooth enamel in combination with personal dose monitoring can help to improve external dose assessment for this cohort. Here, the occupational lifetime external exposure was evaluated individually for 44 nuclear workers of three plants of the Mayak Production Association by EPR measurements of absorbed doses in collected tooth enamel samples. Analysis included consideration of individual background doses in enamel and dose conversion coefficients specific for photon spectra at selected work areas. As a control, background doses were assessed for various age groups by EPR measurements on teeth from non-occupationally exposed Ozyorsk residents. Differences in occupational lifetime doses estimated from the film badges and from enamel for the Mayak workers were found to depend on the type of film badge and the selected plant. For those who worked at the radiochemical processing plant and who were monitored with IFK film badges, the dose was on average 570 mGy larger than estimated from the EPR measurements. However, the average difference was found to be only -4 and 6 mGy for those who were monitored with IFKU film badges and worked at the reactor and the isotope production plant respectively. The discrepancies observed in the dose estimates are attributed to a bias in film badge evaluation.

Adult↗
PubMed2005

LDL induces intracellular signalling and cell migration via atypical LDL-binding protein T-cadherin.

Cadherins are a superfamily of adhesion molecules that mediate Ca(2+)-dependent cell-cell adhesion. T-cadherin (T-cad), a unique glycosylphosphatidylinositol-anchored member of the cadherin superfamily, was initially identified by immunoblotting of vascular cell membranes as an atypical low affinity low density lipoprotein (LDL)-binding protein. It is not known whether this heterophilic interaction is physiologically relevant. Expression of T-cadherin is upregulated in vascular cells during atherosclerosis, restenosis and tumour angiogenesis, conditions characterized by enhanced cell migration and growth. Elevated levels of serum low density lipoproteins (LDL), which result in cholesterol accumulation in vascular wall, is a widely accepted risk factor in atherosclerosis development. Additionally to its metabolic effects, LDL can produce hormone-like effects in a number of cell types. This study has utilized HEK293 cells and L929 cells stably transfected with T-cadherin cDNA to investigate T-cad-dependent responses to LDL. Stable expression of T-cad in both HEK293 and L929 cells results in significantly (p < 0.05) elevated specific surface binding of [I125]-LDL. Compared with mock-transfectants, cells expressing T-cad exhibit significantly (p < 0.01) enhanced LDL-induced mobilization of intracellular Ca(2+)-stores and a significantly (p < 0.01) increased migration toward an LDL gradient (0.1% BSA + 60 microg/ml LDL) in Boyden chamber migration assay. Thus LDL-binding to T-cad is capable of activating physiologically relevant intracellular signaling and functional responses.

Animals↗
PubMed2005

The 3rd international intercomparison on EPR tooth dosimetry: Part 1, general analysis.

The objective of the 3rd International Intercomparison on Electron Paramagnetic Resonance (EPR) Tooth Dosimetry was the evaluation of laboratories performing tooth enamel dosimetry below 300 mGy. Participants had to reconstruct the absorbed dose in tooth enamel from 11 molars, which were cut into two halves. One half of each tooth was irradiated in a 60Co beam to doses in the ranges of 30-100 mGy (5 samples), 100-300 mGy (5 samples), and 300-900 mGy (1 sample). Fourteen international laboratories participated in this intercomparison programme. A first analysis of the results and an overview of the essential features of methods applied in different laboratories are presented. The relative standard deviation of results of all methods was better than 27% for applied doses in the range of 79-704 mGy. In the analysis of the unirradiated tooth halves 8% of the samples were identified as outliers with additional absorbed dose above background dose.

Benchmarking↗
PubMed2005

Spectrum file size optimization for EPR tooth dosimetry.

Spectral acquisition time is one of the limiting factors in electron paramagnetic resonance (EPR) retrospective biodosimetry in teeth. Acquisition times for one sample can be from 2 to 4h. This problem is even more acute for in vivo EPR measurements in L-band. Patients cannot be expected to remain stationary for these lengths of time. In order to overcome this limitation, we investigated the dependence of EPR dose measurements on the number of data points in an EPR spectrum. We have shown that this number could be reduced from 1024 to 256 (factor of 4 reduction in spectral acquisition time) at 5 mT magnetic field sweep without a loss of precision in the dose measurements.

Algorithms↗
PubMed2005

An experimental model for study of sialoglycoproteins of human immunodeficiency virus 1 epitope structures.

Sialic acid (SA) molecules located terminally on retrovirus glycoproteins (gps) play a key role in virus-cell interactions. The specificity of sialylation of Human immunodeficiency virus 1 (HIV-1) gps has not yet been studied. Looking for a convenient and reproducible experimental virus-cell model for studying the problem mentioned above we compared viral sialoglycoprotein (Sgp) patterns in H9/HTLV III B cells chronically infected with laboratory-adapted HIV-1LAI and MT-2 cells acutely infected with the same virus. Cytosols (CSs) and supernatant concentrates (SNs) from these cells and cell cultures, respectively, following N-acetyl-D-[U-14C]-mannosamine ([14C]NAcMan) labeling were subjected to preparative isoelectrofocusing and the obtained fractions were assayed for 14C-incorporation, reverse transcriptase (RT) activity and protein content. Sgp patterns in CSs from the two types of infection were similar. Highly sialylated peaks clustered mainly in the acidic region where the highest 14C-incorporation, RT activity and protein content were found. The 14C-incorporation was higher in CS than in SN. Analysis of CS from MT-2 cells infected with HIV-1 for the markers described above seems to be the experimental approach and model of choice for clinical isolates of HIV-1.

Carbon Radioisotopes↗
PubMed2004

Non-Markovian particle dynamics in continuously controlled quantum gases.

For a quantum gas, being subject to continuous feedback of a macroscopic observable, the single-particle dynamics is studied. Despite feedback-induced particle correlations, it is shown that analytic solutions are obtained by formally extending the single-particle Hilbert space by an auxiliary degree of freedom. The particle's motion is then fed by colored noise, which effectively maps quantum-statistical correlations onto the single particle. Thus, the single particle in the continuously controlled gas follows a non-Markovian trajectory in phase space.

Journal Article↗
PubMed2004

Association analysis of two candidate phospholipase genes that map to the chromosome 15q15.1-15.3 region associated with reading disability.

Molecular genetic studies have suggested a reading disability (RD, dyslexia) susceptibility locus on chromosome 15q. We have previously mapped this locus by association to the region surrounding D15S994. Very little is known about the neurobiological processes involved in RD, and therefore selecting positional candidate genes for analysis based upon function is difficult. Nevertheless we were able to identify two functional candidates based upon existing hypotheses. Both were phospholipase genes, phospholipase C beta 2 (PLCB2) and phospholipase A2, group IVB (cytosolic; PLA2G4B). D15S944 is located within PLCB2 and is 1.6 Mb from PLA2G4B. We examined each gene for association using a mixed direct and indirect association approach, a case (n = 164)/control (n = 174) sample, and a partially overlapping sample of 178 RD parent-proband trios from South Wales and England. Mutation analysis revealed 14 sequence variants in PLCB2 and 33 variants in PLA2G4B. All non-synonymous SNPs were genotyped as were SNPs across each gene with maximum distance between SNPs of 6 kb. Case-control analyses revealed modest evidence (0.01 < P < 0.05) for association between a single variant in PLCB2 and two variants in PLA2G4B. However, association was not confirmed in the family based sample. As the latter sample has previously generated replicated significant evidence for association between RD and markers/haplotypes surrounding D15S944, it should have sufficient power to detect association to variants in susceptibility gene itself. We conclude that neither gene accounts for the association signal we previously observed. As these are the only clear cut functional candidate genes in the region, identification of the putative susceptibility locus for RD on 15q will require more methodical non-hypothesis driven positional cloning approaches.

Alleles↗
PubMed2004

Prevention of experimental autoimmune encephalomyelitis in DA rats by grafting primary skin fibroblasts engineered to express transforming growth factor-beta1.

To determine whether primary fibroblasts producing latent transforming growth factor beta1 (TGF-beta1) are capable of down-regulating experimental autoimmune encephalomyelitis (EAE), a retroviral vector TGF-beta1-pBabe-neo (-5'UTR) was used for efficient gene transfer into primary skin fibroblasts of DA rats. After heat activation, conditioned medium from the transduced fibroblasts was found to inhibit significantly in vitro proliferation of lymphocytes from lymph nodes of DA rats with EAE. Intraperitoneal administration of TGF-beta1-transduced fibroblasts into DA rats during the priming phase of EAE resulted in a significant reduction in mortality and in the mean clinical and EAE scores versus the control immunized animals treated with non-transduced fibroblasts.

Animals↗
PubMed2003

RFP2, c13ORF1, and FAM10A4 are the most likely tumor suppressor gene candidates for B-cell chronic lymphocytic leukemia.

Occurrence of 13q14 deletions between D13S273 and D13S25 in B-cell chronic lymphocytic leukemia (B-CLL) suggests that the region contains a tumor suppressor gene. We constructed a PAC/cosmid contig largely corresponding to a 380-kb 13q14 YAC insert that we found deleted in a high proportion of B-CLL patients. We found seven genes by exon trapping, cDNA screening and analysis/cDNA extension of known expressed sequence tags. One appeared to originate from another region of 13q. Recent publications have focused on two of the genes that most likely do not have a tumor suppressor role. This study evaluates the remaining four genes in the region by mutation scanning and theoretical analysis of putative encoded products. No mutations suggestive of a pathogenic effect were found. The 13q14 deletions may be a consequence of an inherent instability of the region, an idea supported by our finding of a considerable proportion of AluY repeats. Deletion of putative enhancer sequences and/or genes in the region may result in an inactivation of tumor suppression by a haploinsufficiency mechanism. We conclude that RFP2, c13ORF1, and a chromosome 13-specific ST13-like gene, FAM10A4, are the most likely candidates for such a type of B-CLL TSG.

B-Lymphocytes↗
PubMed2003

Lichens as biomonitors of uranium in the Balkan area.

The contribution of the conflict of 1999 to the environmental levels of uranium in the Balkan area was evaluated by means of lichens used as biomonitors. The average U concentration found in lichens in the present study was in line with the values reported for lichens from other countries and well below the levels found in lichens collected in areas with natural or anthropogenic sources of U. Measurement of isotopic ratios 235U/238U allowed to exclude the presence of depleted uranium. According to these results, we could not detect widespread environmental contamination by depleted uranium in the Balkan area.

Environmental Monitoring↗
PubMed2003

Chromosome 22q11 deletions, velo-cardio-facial syndrome and early-onset psychosis. Molecular genetic study.

BACKGROUND: Velo-cardio-facial syndrome (VCFS) is associated with interstitial deletions of chromosome 22q11. About 30% of patients with VCFS have psychosis, and the rate of these deletions in schizophrenia has been reported to be about 1%. Even higher rates of VCFS deletions have been reported for childhood-onset schizophrenia. AIMS: To test the hypothesis that there is an increased rate of VCFS among patients with early-onset psychosis (age at onset <18 years). We screened 192 early-onset patients and 329 patients with adult-onset schizophrenia. METHOD: We genotyped the patients and 444 healthy controls for hemizygosity of five microsatellite markers and one single nucleotide polymorphism that map to the 22q11-deleted region. RESULTS: One patient had a VCFS deletion, confirmed with semi-quantitative polymerase chain reaction. None of the controls showed a pattern of genotypes consistent with hemizygosity. CONCLUSIONS: VCFS may be less frequent among patients with psychosis than previously suggested; this rate is not increased among early-onset patients.

Abnormalities, Multiple↗
PubMed2002

Topologically protected quantum bits using Josephson junction arrays.

All physical implementations of quantum bits (or qubits, the logical elements in a putative quantum computer) must overcome conflicting requirements: the qubits should be manipulable through external signals, while remaining isolated from their environment. Proposals based on quantum optics emphasize optimal isolation, while those following the solid-state route exploit the variability and scalability of nanoscale fabrication techniques. Recently, various designs using superconducting structures have been successfully tested for quantum coherent operation, however, the ultimate goal of reaching coherent evolution over thousands of elementary operations remains a formidable task. Protecting qubits from decoherence by exploiting topological stability is a qualitatively new proposal that holds promise for long decoherence times, but its physical implementation has remained unclear. Here we show how strongly correlated systems developing an isolated twofold degenerate quantum dimer liquid ground state can be used in the construction of topologically stable qubits; we discuss their implementation using Josephson junction arrays. Although the complexity of their architecture challenges the technology base available today, such topological qubits greatly benefit from their built-in fault-tolerance.

Journal Article↗
PubMed2001

The Mus cervicolor MuLV isolate M813 is highly fusogenic and induces a T-cell lymphoma associated with large multinucleated cells.

M813 is a type-C murine leukemia virus (MuLV) isolated from the Asian rodent Mus cervicolor. We have recently demonstrated that M813 defines a distinct MuLV receptor interference group. Here we show that M813 rapidly induces fusion of MuLV-expressing fibroblasts from "without," with syncytia being observed within 1 h after exposure to virus. Infection of fibroblasts with MuLV from all tested receptor-interference groups imparts susceptibility to M813-induced fusion, provided the cells also express the M813 receptor. Syncytium induction is also observed in vivo; mice infected with M813 develop a peripheral T-cell lymphoma, which is associated with large multinucleated cells of macrophage origin. A recombinant Moloney MuLV/M813 chimeric virus demonstrated that syncytium induction is a function of the Env SU protein. We postulate that the highly fusogenic property of M813 is attributable to either its unique receptor usage or sequences in the proline-rich domain of the Env protein.

Animals↗
PubMed2001

Expression of cell adhesion molecule T-cadherin in the human vasculature.

Alterations in expression of surface adhesion molecules on resident vascular and blood-derived cells play a fundamental role in the pathogenesis of cardiovascular disease. Smooth muscle cells (SMCs) have been shown to express T-cadherin (T-cad), an unusual GPI-anchored member of the cadherin family of adhesion molecules. Particular relevance for T-cad in cardiovascular tissues is indicated by our present screen (immunoblotting) of human tissues and organs whereby highest expression of T-cad was found in aorta, carotid, iliac and renal arteries and heart. To explore the (patho)physiological role for T-cad in the vasculature we performed an immunohistochemical analysis of T-cad expression in normal human aorta and atherosclerotic lesions of varying severity. T-cad was present both in the intima and media and was expressed in endothelial cells (ECs), SMCs and pericytes, but not in monocytes/macrophages, foam cells and lymphocytes. In the adventitia T-cad was present in the wall of vasa vasorum and was expressed in ECs, SMCs and pericytes. T-cad was differentially expressed in SMCs from distinct vascular layers of normal aorta (for example, high in the subendothelial (proteoglycan) layer of the intima, low in the musculoelastic intimal layer and in the media), as well as at different stages of lesion progression. In SMCs there was an apparent inverse relationship between the intensities of T-cad and smooth muscle alpha-actin expression, this being most prominent in lesions. The findings suggest a phenotype-associated expression of T-cad which may be relevant to control of the normal vascular architecture and its remodelling during atherogenesis.

Aorta↗
PubMed2001

Induction of vascular endothelial growth factor by nitric oxide in cultured human articular chondrocytes.

We investigated the role of nitric oxide (NO) in the control of vascular endothelial growth factor A (VEGF) gene expression in cultured human articular chondrocytes. Cell treatment with the NO-generating compound nitrosoglutathione (GSNO) caused a significant accumulation of 4.4 kb VEGF mRNA, a major VEGF mRNA isoform expressing in chondrocytes. This is the first demonstration that NO can induce VEGF mRNA expression in chondrocytes. VEGF mRNA level was not affected in cells exposed to dibutyryl cGMP, a non-hydrolyzable analog of cGMP, suggesting that the cGMP system is not involved in NO-dependent transcriptional activation of VEGF gene. The GSNO-stimulated induction of VEGF mRNA was slightly attenuated by MAP protein kinase inhibitors PD98058 and SB203580, but was completely blocked in cells incubated with GSNO in the presence of catalase and superoxide dismutase, enzymes scavenging reactive oxygen species (ROS), or in the presence of thiol-containing antioxidants, N-acetyl cysteine and reduced glutathione. These results suggest that in articular chondrocytes the GSNO-induced VEGF gene transcriptional activation is dependent on endogenous ROS production and oxidative thiol modifications.

Antioxidants↗
PubMed2001

Preparation, physicochemical characterization and pharmacological study of novel ruthenium(III) complexes with imidazole and benzimidazole derivatives.

Complex compounds of ruthenium(III) with 1,2-dimethylimidazole (CAS 1739-84-0), 2-phenylimidazole (CAS 670-96-2) and 2-aminobenzimidazole (CAS 934-32-7) were prepared and were characterised by physicochemical methods. Coordination sites were determined. The complexes were tested for cytotoxic activity using MTT (3-(4,5-dimethyithiazol-2-yl)-2,5-diphenyltetrazolium bromide) dye-reduction assay and the values LD50 were evaluated.

Animals↗