1,791 research outputs found
Mechanisms of cell damage and recovery in cryopreserved freshwater protists
SIGLEAvailable from British Library Document Supply Centre-DSC:DXN015370 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Counterion density profiles at charged flexible membranes
Counterion distributions at charged soft membranes are studied using
perturbative analytical and simulation methods in both weak coupling
(mean-field or Poisson-Boltzmann) and strong coupling limits. The softer the
membrane, the more smeared out the counterion density profile becomes and
counterions pentrate through the mean-membrane surface location, in agreement
with anomalous scattering results. Membrane-charge repulsion leads to a
short-scale roughening of the membrane.Comment: 4 pages, 4 figure
A Targeted Sampling Strategy for Compressive Cryo Focused Ion Beam Scanning Electron Microscopy
Cryo Focused Ion-Beam Scanning Electron Microscopy (cryo FIB-SEM) enables
three-dimensional and nanoscale imaging of biological specimens via a slice and
view mechanism. The FIB-SEM experiments are, however, limited by a slow
(typically, several hours) acquisition process and the high electron doses
imposed on the beam sensitive specimen can cause damage. In this work, we
present a compressive sensing variant of cryo FIB-SEM capable of reducing the
operational electron dose and increasing speed. We propose two Targeted
Sampling (TS) strategies that leverage the reconstructed image of the previous
sample layer as a prior for designing the next subsampling mask. Our image
recovery is based on a blind Bayesian dictionary learning approach, i.e., Beta
Process Factor Analysis (BPFA). This method is experimentally viable due to our
ultra-fast GPU-based implementation of BPFA. Simulations on artificial
compressive FIB-SEM measurements validate the success of proposed methods: the
operational electron dose can be reduced by up to 20 times. These methods have
large implications for the cryo FIB-SEM community, in which the imaging of beam
sensitive biological materials without beam damage is crucial.Comment: Submitted to ICASSP 202
The Potential of Subsampling and Inpainting for Fast Low-Dose Cryo FIB-SEM Imaging and Tomography
Traditional image acquisition for cryo focused ion-beam scanning electron
microscopy tomography often sees thousands of images being captured over a
period of many hours, with immense data sets being produced. When imaging beam
sensitive materials, these images are often compromised by additional
constraints related to beam damage and the devitrification of the material
during imaging, which renders data acquisition both costly and unreliable.
Subsampling and inpainting are proposed as solutions for both of these aspects,
allowing fast and low-dose imaging to take place in the FIB-SEM without an
appreciable low in image quality. In this work, experimental data is presented
which validates subsampling and inpainting as a useful tool for convenient and
reliable data acquisition in a FIB-SEM, with new methods of handling
3-dimensional data being employed in context of dictionary learning and
inpainting algorithms using a newly developed microscope control software and
data recovery algorithm.Comment: In submission to "Microscopy and Microanalysis" journal. Authorship
reviewed from previous submissio
Characterising the chemical and physical properties of phase-change nanodroplets
Phase-change nanodroplets have attracted increasing interest in recent years as ultrasound theranostic nanoparticles. They are smaller compared to microbubbles and they may distribute better in tissues (e.g. in tumours). They are composed of a stabilising shell and a perfluorocarbon core. Nanodroplets can vaporise into echogenic microbubbles forming cavitation nuclei when exposed to ultrasound. Their perfluorocarbon core phase-change is responsible for the acoustic droplet vaporisation. However, methods to quantify the perfluorocarbon core in nanodroplets are lacking. This is an important feature that can help explain nanodroplet phase change characteristics. In this study, we fabricated nanodroplets using lipids shell and perfluorocarbons. To assess the amount of perfluorocarbon in the core we used two methods, 19F-NMR and FTIR. To assess the cavitation after vaporisation we used an ultrasound transducer (1.1MHz) and a high-speed camera. The 19F-NMR based method showed that the fluorine signal correlated accurately with the perfluorocarbon concentration. Using this correlation, we were able to quantify the perfluorocarbon core of nanodroplets. This method was used to assess the content of the perfluorocarbon of the nanodroplets in solutions over time. It was found that perfluoropentane nanodroplets lost their content faster and at higher ratio compared to perfluorohexane nanodroplets. The high-speed camera showed that these nanodroplets have similar cavitation with commercial microbubbles. Nanodroplet characterisation should include perfluorocarbon concentration assessment as critical information for their development
Reply to Comment on Conopeptide-Functionalized Nanoparticles Selectively Antagonize Extrasynaptic N-Methyl-d-aspartate Receptors and Protect Hippocampal Neurons from Excitotoxicity In Vitro
In this manuscript, we provide precise answers to the concerns expressed by Molokanova et al. in their comment. In our reply, we highlight that there is indeed substantial agreement between our study and the one reported in Nano Letters by the Molokanova’s group.1 We believe this is a very important aspect because it proves the validity of the chosen approach, i.e. PEGylated AuNPs carrying NMDAR antagonists and with an overall dimension large enough to prevent their diffusion into the synapse can exclusively antagonize extrasynaptic NMDAR-mediated currents and are thereby neuroprotective
Nanostars Carrying Multifunctional Neurotrophic Dendrimers Protect Neurons in Preclinical In Vitro Models of Neurodegenerative Disorders
A challenge in neurology is the lack of efficient brain-penetrable neuroprotectants targeting multiple disease mechanisms. Plasmonic gold nanostars are promising candidates to deliver standard-of-care drugs inside the brain but have not been trialed as carriers for neuroprotectants. Here, we conjugated custom-made peptide dendrimers (termed H3/H6), encompassing motifs of the neurotrophic S100A4-protein, onto star-shaped and spherical gold nanostructures (H3/H6-AuNS/AuNP) and evaluated their potential as neuroprotectants and interaction with neurons. The H3/H6 nanostructures crossed a model blood-brain barrier, bound to plasma membranes, and induced neuritogenesis with the AuNS, showing higher potency/efficacy than the AuNP. The H3-AuNS/NP protected neurons against oxidative stress, the H3-AuNS being more potent, and against Parkinson's or Alzheimer's disease (PD/AD)-related cytotoxicity. Unconjugated S100A4 motifs also decreased amyloid beta-induced neurodegeneration, introducing S100A4 as a player in AD. Using custom-made dendrimers coupled to star-shaped nanoparticles is a promising route to activate multiple neuroprotective pathways and increase drug potency to treat neurodegenerative disorders
Parasitophorous vacuole poration precedes its rupture and rapid host erythrocyte cytoskeleton collapse in Plasmodium falciparum egress.
In the asexual blood stages of malarial infection, merozoites invade erythrocytes and replicate within a parasitophorous vacuole to form daughter cells that eventually exit (egress) by sequential rupture of the vacuole and erythrocyte membranes. The current model is that PKG, a malarial cGMP-dependent protein kinase, triggers egress, activating malarial proteases and other effectors. Using selective inhibitors of either PKG or cysteine proteases to separately inhibit the sequential steps in membrane perforation, combined with video microscopy, electron tomography, electron energy loss spectroscopy, and soft X-ray tomography of mature intracellular Plasmodium falciparum parasites, we resolve intermediate steps in egress. We show that the parasitophorous vacuole membrane (PVM) is permeabilized 10-30 min before its PKG-triggered breakdown into multilayered vesicles. Just before PVM breakdown, the host red cell undergoes an abrupt, dramatic shape change due to the sudden breakdown of the erythrocyte cytoskeleton, before permeabilization and eventual rupture of the erythrocyte membrane to release the parasites. In contrast to the previous view of PKG-triggered initiation of egress and a gradual dismantling of the host erythrocyte cytoskeleton over the course of schizont development, our findings identify an initial step in egress and show that host cell cytoskeleton breakdown is restricted to a narrow time window within the final stages of egress
Current approaches and future role of high content imaging in safety sciences and drug discovery
High content imaging combines automated microscopy with image analysis approaches to simultaneously quantify multiple phenotypic and/or functional parameters in biological systems. The technology has become an important tool in the fields of safety sciences and drug discovery, because it can be used for mode-of-action identification, determination of hazard potency and the discovery of toxicity targets and biomarkers. In contrast to conventional biochemical endpoints, high content imaging provides insight into the spatial distribution and dynamics of responses in biological systems. This allows the identification of signaling pathways underlying cell defense, adaptation, toxicity and death. Therefore high content imaging is considered a promising technology to address the challenges for the Toxicity testing in the 21st century approach. Currently high content imaging technologies are frequently applied in academia for mechanistic toxicity studies and in pharmaceutical industry for the ranking and selection of lead drug compounds or to identify/confirm mechanisms underlying effects observed in vivo. A recent workshop gathered scientists working on high content imaging in academia, pharmaceutical industry and regulatory bodies with the objective to compile the state-of-the-art of the technology in the different institutions. They defined technical and methodological gaps, addressed the need for quality control, suggested control compounds and acceptance criteria, highlighted cell sources and new readouts and discussed future requirements for regulatory implementation. This review summarizes the discussion, proposed solutions and recommendations of the specialists contributing to the workshop.JRC.I.5-Systems Toxicolog
A generic mechanism in Neisseria meningitidis for enhanced resistance against bactericidal antibodies
The presence of serum bactericidal antibodies is a proven correlate of protection against systemic infection with the important human pathogen Neisseria meningitidis. We have identified three serogroup C N. meningitidis (MenC) isolates recovered from patients with invasive meningococcal disease that resist killing by bactericidal antibodies induced by the MenC conjugate vaccine. None of the patients had received the vaccine, which has been successfully introduced in countries in North America and Europe. The increased resistance was not caused by changes either in lipopolysaccharide sialylation or acetylation of the α2-9–linked polysialic acid capsule. Instead, the resistance of the isolates resulted from the presence of an insertion sequence, IS1301, in the intergenic region (IGR) between the sia and ctr operons, which are necessary for capsule biosynthesis and export, respectively. The insertion sequence led to an increase in the transcript levels of surrounding genes and the amount of capsule expressed by the strains. The increased amount of capsule was associated with down-regulation of the alternative pathway of complement activation, providing a generic mechanism by which the bacterium protects itself against bactericidal antibodies. The strains with IS1301 in the IGR avoided complement-mediated lysis in the presence of bactericidal antibodies directed at the outer membrane protein, PorA, or raised against whole cells
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