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排序方式: 共有1277条查询结果,搜索用时 62 毫秒
1.
Michaela Patila Ioannis V. Pavlidis Evmorfia K. Diamanti Petros Katapodis Dimitrios Gournis Haralampos Stamatis 《Process Biochemistry》2013,48(7):1010-1017
The effect of carbon-based nanomaterials (CBNs), such as multi-wall carbon nanotubes (CNTs) and graphene oxide (GO) nanomaterials functionalized with carboxyl, alkyl and amine groups, on the peroxidase-like activity and structure of cytochrome c (cyt c) was investigated. The catalytic efficiency of cyt c increases up to 78-fold in the presence of graphene oxide and up to 2.5-fold in the presence of other functionalized CBNs. Moreover, the use of functionalized CBNs enhances the thermal stability of the protein as well as its tolerance against hydrogen peroxide up to 2.5-fold. UV–vis and circular dichroism spectroscopy studies suggest that the increase in the peroxidase activity of cyt c in the presence of some functionalized GO nanomaterials, correlates to perturbations of the heme microenvironment, while the secondary structure of the enzyme remains intact. These results indicate that the beneficial effect the functionalized CBNs have on the activity and on the stability of cyt c depends on CBNs geometry and surface functionalization. 相似文献
2.
Jessie S. Jeon Ioannis K. Zervantonakis Seok Chung Roger D. Kamm Joseph L. Charest 《PloS one》2013,8(2)
Tumor cells that disseminate from the primary tumor and survive the vascular system can eventually extravasate across the endothelium to metastasize at a secondary site. In this study, we developed a microfluidic system to mimic tumor cell extravasation where cancer cells can transmigrate across an endothelial monolayer into a hydrogel that models the extracellular space. The experimental protocol is optimized to ensure the formation of an intact endothelium prior to the introduction of tumor cells and also to observe tumor cell extravasation by having a suitable tumor seeding density. Extravasation is observed for 38.8% of the tumor cells in contact with the endothelium within 1 day after their introduction. Permeability of the EC monolayer as measured by the diffusion of fluorescently-labeled dextran across the monolayer increased 3.8 fold 24 hours after introducing tumor cells, suggesting that the presence of tumor cells increases endothelial permeability. The percent of tumor cells extravasated remained nearly constant from1 to 3 days after tumor seeding, indicating extravasation in our system generally occurs within the first 24 hours of tumor cell contact with the endothelium. 相似文献
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Ioannis S. Gousias Alexander Hammers Serena J. Counsell Latha Srinivasan Mary A. Rutherford Rolf A. Heckemann Jo V. Hajnal Daniel Rueckert A. David Edwards 《PloS one》2013,8(4)
We studied methods for the automatic segmentation of neonatal and developing brain images into 50 anatomical regions, utilizing a new set of manually segmented magnetic resonance (MR) images from 5 term-born and 15 preterm infants imaged at term corrected age called ALBERTs. Two methods were compared: individual registrations with label propagation and fusion; and template based registration with propagation of a maximum probability neonatal ALBERT (MPNA). In both cases we evaluated the performance of different neonatal atlases and MPNA, and the approaches were compared with the manual segmentations by means of the Dice overlap coefficient. Dice values, averaged across regions, were 0.81±0.02 using label propagation and fusion for the preterm population, and 0.81±0.02 using the single registration of a MPNA for the term population. Segmentations of 36 further unsegmented target images of developing brains yielded visibly high-quality results. This registration approach allows the rapid construction of automatically labeled age-specific brain atlases for neonates and the developing brain. 相似文献
5.
Missing data are unavoidable in environmental epidemiologic surveys. The aim of this study was to compare methods for handling large amounts of missing values: omission of missing values, single and multiple imputations (through linear regression or partial least squares regression), and a fully Bayesian approach. These methods were applied to the PARIS birth cohort, where indoor domestic pollutant measurements were performed in a random sample of babies'' dwellings. A simulation study was conducted to assess performances of different approaches with a high proportion of missing values (from 50% to 95%). Different simulation scenarios were carried out, controlling the true value of the association (odds ratio of 1.0, 1.2, and 1.4), and varying the health outcome prevalence. When a large amount of data is missing, omitting these missing data reduced statistical power and inflated standard errors, which affected the significance of the association. Single imputation underestimated the variability, and considerably increased risk of type I error. All approaches were conservative, except the Bayesian joint model. In the case of a common health outcome, the fully Bayesian approach is the most efficient approach (low root mean square error, reasonable type I error, and high statistical power). Nevertheless for a less prevalent event, the type I error is increased and the statistical power is reduced. The estimated posterior distribution of the OR is useful to refine the conclusion. Among the methods handling missing values, no approach is absolutely the best but when usual approaches (e.g. single imputation) are not sufficient, joint modelling approach of missing process and health association is more efficient when large amounts of data are missing. 相似文献
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Much attention has recently been given to the statistical significance of topological features observed in biological networks. Here, we consider residue interaction graphs (RIGs) as network representations of protein structures with residues as nodes and inter-residue interactions as edges. Degree-preserving randomized models have been widely used for this purpose in biomolecular networks. However, such a single summary statistic of a network may not be detailed enough to capture the complex topological characteristics of protein structures and their network counterparts. Here, we investigate a variety of topological properties of RIGs to find a well fitting network null model for them. The RIGs are derived from a structurally diverse protein data set at various distance cut-offs and for different groups of interacting atoms. We compare the network structure of RIGs to several random graph models. We show that 3-dimensional geometric random graphs, that model spatial relationships between objects, provide the best fit to RIGs. We investigate the relationship between the strength of the fit and various protein structural features. We show that the fit depends on protein size, structural class, and thermostability, but not on quaternary structure. We apply our model to the identification of significantly over-represented structural building blocks, i.e., network motifs, in protein structure networks. As expected, choosing geometric graphs as a null model results in the most specific identification of motifs. Our geometric random graph model may facilitate further graph-based studies of protein conformation space and have important implications for protein structure comparison and prediction. The choice of a well-fitting null model is crucial for finding structural motifs that play an important role in protein folding, stability and function. To our knowledge, this is the first study that addresses the challenge of finding an optimized null model for RIGs, by comparing various RIG definitions against a series of network models. 相似文献
8.
Panayiotis D. Ziakas Ioannis M. Zacharioudakis Fainareti N. Zervou Christos Grigoras Elina Eleftheria Pliakos Eleftherios Mylonakis 《PloS one》2015,10(2)
BackgroundThe impact of Clostridium difficile colonization in C. difficile infection (CDI) is inadequately explored. As a result, asymptomatic carriage is not considered in the development of infection control policies and the burden of carrier state in long-term care facilities (LTCFs) is unknown.PurposeTo explore the epidemiology of C. difficile colonization in LTCFs, identify predisposing factors and describe its impact on healthcare management.ResultsBased on data from 9 eligible studies that met the specified criteria and included 1,371 subjects, we found that 14.8% (95%CI 7.6%-24.0%) of LTCF residents are asymptomatic carriers of toxigenic C. difficile. Colonization estimates were significantly higher in facilities with prior CDI outbreak (30.1% vs. 6.5%, p = 0.01). Patient history of CDI (OR 6.07; 95% CI 2.06–17.88; effect derived from 3 studies), prior hospitalization (OR 2.11; 95% CI 1.08–4.13; derived from 3 studies) and antimicrobial use within previous 3 months (OR 3.68; 95% CI 2.04–6.62; derived from 4 studies) were associated with colonization. The predicted colonization rate at admission was 8.9%.ConclusionAsymptomatic carriage of toxigenic C. difficile represents a significant burden in LTCFs and is associated with prior CDI outbreaks in the facility, a history of CDI, prior hospitalization and antimicrobial use. These findings can impact infection control measures at LTCFs. 相似文献
9.
Weijun Ke Lingling Mao Constantinos C. Stoumpos Justin Hoffman Ioannis Spanopoulos Aditya D. Mohite Mercouri G. Kanatzidis 《Liver Transplantation》2019,9(10)
Hybrid halide 2D perovskites deserve special attention because they exhibit superior environmental stability compared with their 3D analogs. The closer interlayer distance discovered in 2D Dion–Jacobson (DJ) type of halide perovskites relative to 2D Ruddlesden–Popper (RP) perovskites implies better carrier charge transport and superior performance in solar cells. Here, the structure and properties of 2D DJ perovskites employing 3‐(aminomethyl)piperidinium (3AMP2+) as the spacing cation and a mixture of methylammonium (MA+) and formamidinium (FA+) cations in the perovskite cages are presented. Using single‐crystal X‐ray crystallography, it is found that the mixed‐cation (3AMP)(MA0.75FA0.25)3Pb4I13 perovskite has a narrower bandgap, less distorted inorganic framework, and larger Pb? I? Pb angles than the single‐cation (3AMP)(MA)3Pb4I13. Furthermore, the (3AMP)(MA0.75FA0.25)3Pb4I13 films made by a solvent‐engineering method with a small amount of hydriodic acid have a much better film morphology and crystalline quality and more preferred perpendicular orientation. As a result, the (3AMP)(MA0.75FA0.25)3Pb4I13‐based solar cells exhibit a champion power conversion efficiency of 12.04% with a high fill factor of 81.04% and a 50% average efficiency improvement compared to the pristine (3AMP)(MA)3Pb4I13 cells. Most importantly, the 2D DJ 3AMP‐based perovskite films and devices show better air and light stability than the 2D RP butylammonium‐based perovskites and their 3D analogs. 相似文献
10.
Maria Troullinaki Vasileia‐Ismini Alexaki Ioannis Mitroulis Anke Witt Anne Klotzschevon Ameln Kyoung‐Jin Chung Triantafyllos Chavakis Matina Economopoulou 《Journal of cellular and molecular medicine》2019,23(4):2362-2371
The mechanism underlying vasoproliferative retinopathies like retinopathy of prematurity (ROP) is hypoxia‐triggered neovascularisation. Nerve growth factor (NGF), a neurotrophin supporting survival and differentiation of neuronal cells may also regulate endothelial cell functions. Here we studied the role of NGF in pathological retinal angiogenesis in the course of the ROP mouse model. Topical application of NGF enhanced while intraocular injections of anti‐NGF neutralizing antibody reduced pathological retinal vascularization in mice subjected to the ROP model. The pro‐angiogenic effect of NGF in the retina was mediated by inhibition of retinal endothelial cell apoptosis. In vitro, NGF decreased the intrinsic (mitochondria‐dependent) apoptosis in hypoxia‐treated human retinal microvascular endothelial cells and preserved the mitochondrial membrane potential. The anti‐apoptotic effect of NGF was associated with increased BCL2 and reduced BAX, as well as with enhanced ERK and AKT phosphorylation, and was abolished by inhibition of the AKT pathway. Our findings reveal an anti‐apoptotic role of NGF in the hypoxic retinal endothelium, which is involved in promoting pathological retinal vascularization, thereby pointing to NGF as a potential target for proliferative retinopathies. 相似文献