1,304 research outputs found
Cell bystander effect induced by radiofrequency electromagnetic fields and magnetic nanoparticles
Induced effects by direct exposure to ionizing radiation (IR) are a central
issue in many fields like radiation protection, clinic diagnosis and
oncological therapies. Direct irradiation at certain doses induce cell death,
but similar effects can also occur in cells no directly exposed to IR, a
mechanism known as bystander effect. Non-IR (radiofrequency waves) can induce
the death of cells loaded with MNPs in a focused oncological therapy known as
magnetic hyperthermia. Indirect mechanisms are also able to induce the death of
unloaded MNPs cells. Using in vitro cell models, we found that colocalization
of the MNPs at the lysosomes and the non-increase of the temperature induces
bystander effect under non-IR. Our results provide a landscape in which
bystander effects are a more general mechanism, up to now only observed and
clinically used in the field of radiotherapy.Comment: 16 pages, 4 figures, submitted to International Journal of Radiation
Biolog
Protein adsorption onto Fe3O4 nanoparticles with opposite surface charge and its impact on cell uptake
Nanoparticles (NPs) engineered for biomedical applications are meant to be in
contact with protein-rich physiological fluids. These proteins are usually
adsorbed onto the NP surface, forming a swaddling layer called protein corona
that influences cell internalization. We present a study on protein adsorption
onto different magnetic NPs (MNPs) when immersed in cell culture medium, and
how these changes affect the cellular uptake. Two colloids with magnetite cores
of 25 nm, same hydrodynamic size and opposite surface charge were in situ
coated with (a) positive polyethyleneimine (PEI-MNPs) and (b) negative
poly(acrylic acid) (PAA-MNPs). After few minutes of incubation in cell culture
medium the wrapping of the MNPs by protein adsorption resulted in a 5-fold size
increase. After 24 h of incubation large MNP-protein aggregates with
hydrodynamic sizes 1500 to 3000 nm (PAA-MNPs and PEI-MNPs respectively) were
observed. Each cluster contained an estimated number of magnetic cores between
450 and 1000, indicating the formation of large aggregates with a "plum
pudding" structure of MNPs embedded into a protein network of negative surface
charge irrespective of the MNP_core charge. We demonstrated that PEI-MNPs are
incorporated in much larger amounts than the PAA-MNPs units. Quantitative
analysis showed that SH-SY5Y cells can incorporate 100 per cent of the added
PEI-MNPs up to about 100 pg per cell, whereas for PAA-MNPs the uptake was less
than 50 percent. The final cellular distribution showed also notable
differences regarding partial attachment to the cell membrane. These results
highlight the need to characterize the final properties of MNPs after protein
adsorption in biological media, and demonstrate the impact of these properties
on the internalization mechanisms in neural cells.Comment: 32 pages, 10 figure
Magnetic hyperthermia in single-domain monodisperse FeCo nanoparticles: Evidences for Stoner-Wohlfarth behaviour and large losses
We report on hyperthermia measurements on a colloidal solution of 15 nm
monodisperse FeCo nanoparticles (NPs). Losses as a function of the magnetic
field display a sharp increase followed by a plateau, which is what is expected
for losses of ferromagnetic single-domain NPs. The frequency dependence of the
coercive field is deduced from hyperthermia measurement and is in quantitative
agreement with a simple model of non-interacting NPs. The measured losses (1.5
mJ/g) compare to the highest of the literature, though the saturation
magnetization of the NPs is well below the bulk one.Comment: 14 pages, 3 figure
Application of magnetically induced hyperthermia on the model protozoan Crithidia fasciculata as a potential therapy against parasitic infections
Magnetic hyperthermia is currently an EU-approved clinical therapy against
tumor cells that uses magnetic nanoparticles under a time varying magnetic
field (TVMF). The same basic principle seems promising against trypanosomatids
causing Chagas disease and sleeping sickness, since therapeutic drugs available
display severe side effects and drug-resistant strains. However, no
applications of this strategy against protozoan-induced diseases have been
reported so far. In the present study, Crithidia fasciculata, a widely used
model for therapeutic strategies against pathogenic trypanosomatids, was
targeted with Fe_{3}O_{4} magnetic nanoparticles (MNPs) in order to remotely
provoke cell death using TVMFs. The MNPs with average sizes of d approx. 30 nm
were synthesized using a precipitation of FeSO_{4}4 in basic medium. The MNPs
were added to Crithidia fasciculata choanomastigotes in exponential phase and
incubated overnight. The amount of uploaded MNPs per cell was determined by
magnetic measurements. Cell viability using the MTT colorimetric assay and flow
cytometry showed that the MNPs were incorporated by the cells with no
noticeable cell-toxicity effects. When a TVMF (f = 249 kHz, H = 13 kA/m) was
applied to MNP-bearing cells, massive cell death was induced via a
non-apoptotic mechanism. No effects were observed by applying a TVMF on control
(without loaded MNPs) cells. No macroscopic rise in temperature was observed in
the extracellular medium during the experiments. Scanning Electron Microscopy
showed morphological changes after TVMF experiments. These data indicate (as a
proof of principle) that intracellular hyperthermia is a suitable technology to
induce the specific death of protozoan parasites bearing MNPs. These findings
expand the possibilities for new therapeutic strategies that combat parasitic
infections.Comment: 9 pages, four supplementary video file
Field Dependence of Blocking Temperature in Magnetite Nanoparticles
Spherical magnetite nanoparticles having average particle size = 5 nm
have been synthesized by coprecipitation of Fe(II) and Fe(III) salts in KOH
with Polyvinylalcohol (PVA). The resulting dry powder displayed
superparamgnetic (SPM) behaviour at room temperature, with a transition to a
blocked state at TB ~ 45 K for applied field Happ = 500 Oe. The effect of
dipolar interactions was investigated by measuring the dependence of TB on the
applied field Hap and driven ac field in susceptibility data. A thermally
activated model has been used to fit the dynamic data to obtain the
single-particle energy barriers Ea = KeffV, allowing us to estimate the
contributions of dipolar interactions to the single-particle effective magnetic
anisotropy Keff. We have measured the dependence of TB with Hap in order to
draw the transition contours of a H-T diagram. Two different regimes are found
for the (TB-T0) ~H{\lambda} dependence at low and high fields, that can be
understood within a pure SPM relaxation-time (N\'eel-Brown) landscape. The
TB(H) data shows a crossover from {\lambda} = 2/3 to {\lambda} ~2 for applied
magnetic fields of \approx 550 Oe.Comment: 6 pages, 4 figure
Offender's Narratives on Criminal Desistance While Serving a Prison Sentence
This study analyzes the early desistance narratives of a sample of 44 male offenders, between 20 and 50 years old, incarcerated in Spain for serious crimes. In particular, two types of the inmatesâ stories are evaluated: 1) their narratives of personal change toward a non-criminal life (identity change, perceived self-efficacy and willingness for desistance); 2) their perceptions on those transitional or facilitator factors for desistance available to them (new learning, support and social bonding). Participantsâ accounts show how many subjects, despite being still in prison, claim to have experienced favorable changes and have different facilitating factors to abandon their previous criminal life. Despite this, such early narratives of withdrawal are not exempt from ambivalences and contradictions, both between subjects and within subjects. The process of desistance and their contradictions was interpreted, in accordance with the reviewed literature, as a long journey which is often traversed in a circular and zigzagging manner. Finally, it has been discussed how the correctional system should play a major role in facilitating the personal changes and the social support necessary for the ex-offendersâ journey to desistance to be successful
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