135 research outputs found
Cell targeting and imaging using magnetic nanoparticles
BACKGROUND AND AIMS. The success of stem cell therapies partly depends on the
ability to deliver the cells to the site of injury. Circulating endothelial progenitor cells
(EPCs) are involved in physiological processes such as vascular re-endothelialisation
and post-ischaemic neovascularisation and have been utilised in several clinical trials.
Superparamagnetic iron oxide particles have previously been used to label and track
cells using magnetic resonance imaging (MRI), as well as to magnetically attract drugs
and cells to desired sites. The aim of this PhD was to develop a methodology to
magnetically attract EPCs, labelled with a clinically approved iron oxide agent, to a site
of arterial injury using magnetic fields originating outside the body.
METHODS AND RESULTS. Human EPCs were cultured in the presence of iron oxide
superparamagnetic nanoparticles. A labelling method was developed that retained cell
survival and differentiation, as indicated by metabolic activity and flow cytometry
assays, as well as MRI visibility. Finite element modelling (FEM) computer simulations
were performed to investigate the interaction of magnetic forces with hydrodynamic
drag forces. FEM indicated successful external magnetic cell targeting from a vessel
with flow rate similar to a rat common carotid artery; correspondingly there was a 6-
fold increase in cell capture in an in vitro flow system. Angioplasty was performed on
rat common carotid arteries to denude the endothelium and EPCs were administered
with and without the presence of the external magnetic device during a 10 minute period
of flow cessation. Targeting enhanced cell retention at the site of injury by 5-fold.
CONCLUSIONS. Using an externally applied magnetic device, it is possible to enhance
EPC localisation in a flowing sytem in vitro and to a flow-isolated site of common
carotid artery injury in vivo, without affecting cell viability or differentiation in culture.
This technology could be more widely adapted to localise and monitor cells in other
organs and may provide a useful tool for systemic injection of cell therapies
Hyperthermia treatment of tumors by mesenchymal stem cell-delivered superparamagnetic iron oxide nanoparticles.
Magnetic hyperthermia - a potential cancer treatment in which superparamagnetic iron oxide nanoparticles (SPIONs) are made to resonantly respond to an alternating magnetic field (AMF) and thereby produce heat - is of significant current interest. We have previously shown that mesenchymal stem cells (MSCs) can be labeled with SPIONs with no effect on cell proliferation or survival and that within an hour of systemic administration, they migrate to and integrate into tumors in vivo. Here, we report on some longer term (up to 3 weeks) post-integration characteristics of magnetically labeled human MSCs in an immunocompromized mouse model. We initially assessed how the size and coating of SPIONs dictated the loading capacity and cellular heating of MSCs. Ferucarbotran(®) was the best of those tested, having the best like-for-like heating capability and being the only one to retain that capability after cell internalization. A mouse model was created by subcutaneous flank injection of a combination of 0.5 million Ferucarbotran-loaded MSCs and 1.0 million OVCAR-3 ovarian tumor cells. After 2 weeks, the tumors reached ~100 µL in volume and then entered a rapid growth phase over the third week to reach ~300 µL. In the control mice that received no AMF treatment, magnetic resonance imaging (MRI) data showed that the labeled MSCs were both incorporated into and retained within the tumors over the entire 3-week period. In the AMF-treated mice, heat increases of ~4°C were observed during the first application, after which MRI indicated a loss of negative contrast, suggesting that the MSCs had died and been cleared from the tumor. This post-AMF removal of cells was confirmed by histological examination and also by a reduced level of subsequent magnetic heating effect. Despite this evidence for an AMF-elicited response in the SPION-loaded MSCs, and in contrast to previous reports on tumor remission in immunocompetent mouse models, in this case, no significant differences were measured regarding the overall tumor size or growth characteristics. We discuss the implications of these results on the clinical delivery of hyperthermia therapy to tumors and on the possibility that a preferred therapeutic route may involve AMF as an adjuvant to an autologous immune response
Transferability of Insights from Fundamental Investigations into Practical Applications of Prechamber Combustion Systems
Efforts to reduce CO2 emissions from spark ignition engines have driven engine development
to lean-burn or high-dilution operation, which results in high combustion variability
as well as increased unburned hydrocarbon emissions. A widely used technology
to reduce these issues are prechamber ignition systems, in which the external ignition
source is located in a separate small volume, connected to the main chamber via small
orifices. This setup allows for design of favourable ignition conditions near the ignition
source, which results in fast and repeatable early flame propagation. The pressure
increase resulting from combustion taking place inside the prechamber leads to the
ejection of jets containing hot combustion products and possibly active radicals into
the main chamber, which ignite the lean or diluted mixture; this process is often dubbed
turbulent jet ignition or TJI. The use of TJI systems in engines allows the combustion
of very lean/diluted mixtures, resulting in higher efficiencies and lower NOx emissions.
In this work we shed light into the importance of quenching for practical applications
involving turbulent jet ignition. This is achieved through optical investigations in a generic,
constant volume test-rig, combined with zero-dimensional (0-D) model calculations.
The 0-D model is applied to the generic setup and in real engine applications
under varying operating conditions, in order to highlight the relative importance of
quenching under the various thermochemical conditions encountered. The results indicate
that thermal quenching in the nozzle should not be expected due to the small
flame thickness under high pressure encountered in internal combustion engines. Nevertheless,
under the jet mixing conditions expected in engines, hydrodynamic quenching
due to mixing of burned products with unburned (cold) main chamber mixture can
be expected. In most engine conditions, the re-ignition process of the initially quenched
jet after their exit from the prechamber is expected to be so fast, that quenching will
not be apparent in most measurements
Hyperthermia treatment of tumors by mesenchymal stem cell-delivered superparamagnetic iron oxide nanoparticles
Magnetic hyperthermia – a potential cancer treatment in which superparamagnetic iron oxide nanoparticles (SPIONs) are made to resonantly respond to an alternating magnetic field (AMF) and thereby produce heat – is of significant current interest. We have previously shown that mesenchymal stem cells (MSCs) can be labeled with SPIONs with no effect on cell proliferation or survival and that within an hour of systemic administration, they migrate to and integrate into tumors in vivo. Here, we report on some longer term (up to 3 weeks) post-integration characteristics of magnetically labeled human MSCs in an immunocompromized mouse model. We initially assessed how the size and coating of SPIONs dictated the loading capacity and cellular heating of MSCs. Ferucarbotran® was the best of those tested, having the best like-for-like heating capability and being the only one to retain that capability after cell internalization. A mouse model was created by subcutaneous flank injection of a combination of 0.5 million Ferucarbotran-loaded MSCs and 1.0 million OVCAR-3 ovarian tumor cells. After 2 weeks, the tumors reached ~100 µL in volume and then entered a rapid growth phase over the third week to reach ~300 µL. In the control mice that received no AMF treatment, magnetic resonance imaging (MRI) data showed that the labeled MSCs were both incorporated into and retained within the tumors over the entire 3-week period. In the AMF-treated mice, heat increases of ~4°C were observed during the first application, after which MRI indicated a loss of negative contrast, suggesting that the MSCs had died and been cleared from the tumor. This post-AMF removal of cells was confirmed by histological examination and also by a reduced level of subsequent magnetic heating effect. Despite this evidence for an AMF-elicited response in the SPION-loaded MSCs, and in contrast to previous reports on tumor remission in immunocompetent mouse models, in this case, no significant differences were measured regarding the overall tumor size or growth characteristics. We discuss the implications of these results on the clinical delivery of hyperthermia therapy to tumors and on the possibility that a preferred therapeutic route may involve AMF as an adjuvant to an autologous immune response
Lipid peptide nanocomplexes for gene delivery and magnetic resonance imaging in the brain.
Gadolinium-labelled nanocomplexes offer prospects for the development of real-time, non-invasive imaging strategies to visualise the location of gene delivery by MRI. In this study, targeted nanoparticle formulations were prepared comprising a cationic liposome (L) containing a Gd-chelated lipid at 10, 15 and 20% by weight of total lipid, a receptor-targeted, DNA-binding peptide (P) and plasmid DNA (D), which electrostatically self-assembled into LPD nanocomplexes. The LPD formulation containing the liposome with 15% Gd-chelated lipid displayed optimal peptide-targeted, transfection efficiency. MRI conspicuity peaked at 4h after incubation of the nanocomplexes with cells, suggesting enhancement by cellular uptake and trafficking. This was supported by time course confocal microscopy analysis of transfections with fluorescently-labelled LPD nanocomplexes. Gd-LPD nanocomplexes delivered to rat brains by convection-enhanced delivery were visible by MRI at 6 h, 24 h and 48 h after administration. Histological brain sections analysed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) confirmed that the MRI signal was associated with the distribution of Gd(3+) moieties and differentiated MRI signals due to haemorrhage. The transfected brain cells near the injection site appeared to be mostly microglial. This study shows the potential of Gd-LPD nanocomplexes for simultaneous delivery of contrast agents and genes for real-time monitoring of gene therapy in the brain
Directing cell therapy to anatomic target sites in vivo with magnetic resonance targeting
Cell-based therapy exploits modified human cells to treat diseases but its targeted application
in specific tissues, particularly those lying deep in the body where direct injection is not
possible, has been problematic. Here we use a magnetic resonance imaging (MRI) system to
direct macrophages carrying an oncolytic virus, Seprehvir, into primary and metastatic tumour
sites in mice. To achieve this, we magnetically label macrophages with super-paramagnetic
iron oxide nanoparticles and apply pulsed magnetic field gradients in the direction of the
tumour sites. Magnetic resonance targeting guides macrophages from the bloodstream into
tumours, resulting in increased tumour macrophage infiltration and reduction in tumour
burden and metastasis. Our study indicates that clinical MRI scanners can not only track the
location of magnetically labelled cells but also have the potential to steer them into one or
more target tissues
Trammel net catch species composition, catch rates and metiers in southern European waters: A multivariate approach
We identified and quantified the effect of season, depth, and inner and outer panel mesh size on the trammel net catch species composition and catch rates in four southern European areas (Northeast Atlantic: Basque Country, Spain; Algarve, Portugal; Gulf of Cadiz, Spain; Mediterranean: Cyclades, Greece), all of which are characterised by important trammel net fisheries. In each area, we conducted, in 1999-2000, seasonal, experimental fishing trials at various depths with trammel nets of six different inner/outer panel mesh combinations (i.e., two large outer panel meshes and three small inner panel meshes). Overall, our study covered some of the most commonly used inner panel mesh sizes, ranging from 40 to 140 mm (stretched). We analysed the species composition and catch rates of the different inner/outer panel combinations with regression, multivariate analysis (cluster analysis and multidimensional scaling) and other 'community' techniques (number of species, dominance curves). All our analyses indicated that the outer panel mesh sizes used in the present study did not significantly affect the catch characteristics in terms of number of species, catch rates and species composition. Multivariate analyses and seasonal dominance plots indicated that in Basque, Algarve and Cyclades waters, where sampling covered wide depth ranges, both season and depth strongly affected catch species compositions. For the Gulf of Cadiz, where sampling was restricted to depths 10-30 m, season was the only factor affecting catch species composition and thus group formation. In contrast, the inner panel mesh size did not generally affect multidimensional group formation in all areas but affected the dominance of the species caught in the Algarve and the Gulf of Cadiz. Multivariate analyses also revealed 11 different metiers (i.e., season-depth-species-inner panel mesh size combinations) in the four areas. This clearly indicated the existence of trammel net 'hot spots', which represent essential habitats (e.g., spawning, nursery or wintering grounds) of the life history of the targeted and associated species. The number of specimens caught declined significantly with inner panel mesh size in all areas. We attributed this to the exponential decline in abundance with size, both within- and between-species. In contrast, the number of species caught in each area was not related to the inner mesh size. This was unexpected and might be a consequence of the wide size-selective range of trammel nets. (c) 2006 Elsevier B.V All rights reserved
Surface radio-mineralisation mediates chelate-free radiolabelling of iron oxide nanoparticles
We introduce the concept of surface radio-mineralisation (SRM) to describe the chelate-free radiolabelling of iron-oxide and ferrite nanoparticles. We demonstrate the effectiveness of SRM with both 111In and 89Zr for bare, polymer-matrix multicore, and surface-functionalised magnetite/maghemite nanoparticles; and for bare Y3Fe5O12 nanoparticles. By analogy with geological mineralisation (the hydrothermal deposition of metals as minerals in ore bodies or lodes) we demonstrate that the heat-induced and aqueous SRM process deposits radiometal-oxides onto the nanoparticle or core surfaces, passing through the matrix or coating if present, without changing the size, structure, or magnetic properties of the nanoparticle or core. We show in a mouse model followed over 7 days that the SRM is sufficient to allow quantitative, non-invasive, prolonged, whole-body localisation of injected nanoparticles with nuclear imaging
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