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F Gazeau

Publications and source records attributed to F Gazeau.

12 recordsLinked to original sources
PubMed2006

Signaling through the phosphatidylinositol 3-kinase regulates mechanotaxis induced by local low magnetic forces in Entamoeba histolytica.

In micro-organisms, as well as in metazoan cells, cellular polarization and directed migration are finely regulated by external stimuli, including mechanical stresses. The mechanisms sustaining the transduction of such external stresses into intracellular biochemical signals remain mainly unknown. Using an external magnetic tip, we generated a magnetic field gradient that allows migration analysis of cells submitted to local low-intensity magnetic forces (50 pN). We applied our system to the amoeba Entamoeba histolytica. Indeed, motility and chemotaxis are key activities that allow this parasite to invade and destroy the human tissues during amoebiasis. The magnetic force was applied either inside the cytoplasm or externally at the rear pole of the amoeba. We observed that the application of an intracellular force did not affect cell polarization and migration, whereas the application of the force at the rear pole of the cell induced a persistent polarization and strongly directional motion, almost directly opposed to the magnetic force. This phenomenon was completely abolished when phosphatidylinositol 3-kinase activity was inhibited by wortmanin. This result demonstrated that the applied mechanical stimulus was transduced and amplified into an intracellular biochemical signal, a process that allows such low-intensity force to strongly modify the migration behavior of the cell.

Animals↗
PubMed2005

Evaluation of tumoral enhancement by superparamagnetic iron oxide particles: comparative studies with ferumoxtran and anionic iron oxide nanoparticles.

This study was designed to compare tumor enhancement by superparamagnetic iron oxide particles, using anionic iron oxide nanoparticles (AP) and ferumoxtran. In vitro, relaxometry and media with increasing complexity were used to assess the changes in r2 relaxivity due to cellular internalization. In vivo, 26 mice with subcutaneously implanted tumors were imaged for 24 h after injection of particles to describe kinetics of enhancement using T1 spin echo, T2 spin echo, and T2 fast spin echo sequences. In vitro, the r2 relaxivity decreased over time (0-4 h) when AP were uptaken by cells. The loss of r2 relaxivity was less pronounced with long (Hahn Echo) than short (Carr-Purcell-Meiboom-Gill) echo time sequences. In vivo, our results with ferumoxtran showed an early T2 peak (1 h), suggesting intravascular particles and a second peak in T1 (12 h), suggesting intrainterstitial accumulation of particles. With AP, the late peak (24 h) suggested an intracellular accumulation of particles. In vitro, anionic iron oxide nanoparticles are suitable for cellular labeling due to a high cellular uptake. Conversely, in vivo, ferumoxtran is suitable for passive targeting of tumors due to a favorable biodistribution.

Adenocarcinoma↗
PubMed2003

Deformation of intracellular endosomes under a magnetic field.

We present a non-invasive method to monitor the membrane tension of intracellular organelles using a magnetic field as an external control parameter. By exploiting the spontaneous endocytosis of anionic colloidal ferromagnetic nanoparticles, we obtain endosomes possessing a superparamagnetic lumen in eukaryotic cells. Initially flaccid, the endosomal membrane undulates because of thermal fluctuations, restricted in zero field by the resting tension and the curvature energy of the membrane. When submitted to a uniform magnetic field, the magnetized endosomes elongate along the field, resulting in the flattening of the entropic membrane undulations. The quantification of the endosome deformation for different magnetic fields allows in situ measurement of the resting tension and the bending stiffness of the membrane enclosing the intracellular organelle.

Cell Membrane↗
PubMed2003

Rotational magnetic endosome microrheology: viscoelastic architecture inside living cells.

The previously developed technique of magnetic rotational microrheology [Phys. Rev. E 67, 011504 (2003)] is proposed to investigate the rheological properties of the cell interior. An endogeneous magnetic probe is obtained inside living cells by labeling intracellular compartments with magnetic nanoparticles, following the endocytosis mechanism, the most general pathway used by eucaryotic cells to internalize substances from an extracellular medium. Primarily adsorbed on the plasma membrane, the magnetic nanoparticles are first internalized within submicronic membrane vesicles (100 nm diameter) to finally concentrate inside endocytotic intracellular compartments (0.6 microm diameter). These magnetic endosomes attract each other and form chains within the living cell when submitted to an external magnetic field. Here we demonstrate that these chains of magnetic endosomes are valuable tools to probe the intracellular dynamics at very local scales. The viscoelasticity of the chain microenvironment is quantified in terms of a viscosity eta and a relaxation time tau by analyzing the rotational dynamics of each tested chain in response to a rotation of the external magnetic field. The viscosity eta governs the long time flow of the medium surrounding the chains and the relaxation time tau reflects the proportion of solidlike versus liquidlike behavior (tau=eta/G, where G is the high-frequency shear modulus). Measurements in HeLa cells show that the cell interior is a highly heterogeneous structure, with regions where chains are embedded inside a dense viscoelastic matrix and other domains where chains are surrounded by a less rigid viscoelastic material. When one compound of the cell cytoskeleton is disrupted (microfilaments or microtubules), the intracellular viscoelasticity becomes less heterogeneous and more fluidlike, in the sense of both a lower viscosity and a lower relaxation time.

Adsorption↗
PubMed2003

Cell internalization of anionic maghemite nanoparticles: quantitative effect on magnetic resonance imaging.

Anionic iron oxide nanoparticles are efficiently internalized into macrophages where they concentrate within micrometric endosomes, conferring on them a high magnetic susceptibility. The uptake of anionic maghemite nanoparticles by macrophages was quantified by an electron spin resonance (ESR) experiment. MR spin-echo sequences were performed with various TEs and TRs. The contrast enhancement was compared between two types of agarose phantoms with the same equivalent ferrite concentrations but containing either dispersed isolated nanoparticles or magnetically labeled macrophages. It is shown that the intracellular confinement of maghemite nanoparticles within micrometric endosomes results in a significant decrease of the longitudinal relaxivity and a moderate decrease of the transverse relaxivity compared to the relaxivities of the dispersed isolated nanoparticles. As a consequence, the signature of endosomal magnetic labeling consists of a negative contrast on T(1)-weighted images in the whole ferrite concentration range, whereas the presence of extracellular isolated nanoparticles can result in a positive enhancement.

Animals↗
PubMed2003

Intracellular uptake of anionic superparamagnetic nanoparticles as a function of their surface coating.

A new class of superparamagnetic nanoparticles bearing negative surface charges is presented. These anionic nanoparticles show a high affinity for the cell membrane and, as a consequence, are captured by cells with an efficiency three orders of magnitude higher than the widely used dextran-coated iron oxide nanoparticles. The surface coating of anionic particle with albumin strongly reduces the non specific interactions with the plasma membrane as well as the overall cell uptake and at the same time restores the ability to induce specific interactions with targeted cells by the coadsorption on the particle surface of a specific ligand. Kinetics of cellular particle uptake for different cell lines are quantitated using two new complementary assays (Magnetophoresis and Electron Spin Resonance).

Animals↗
PubMed2002

Binding of biological effectors on magnetic nanoparticles measured by a magnetically induced transient birefringence experiment.

We have investigated the relaxation of the magnetically induced birefringence in a suspension of magnetic nanoparticles in order to detect the binding reaction of polyclonal antibodies on the particle surface. The birefringence relaxation is driven by the rotational diffusion of the complex formed by the magnetic nanoparticles bound to the antibody and thus is directly related to the hydrodynamic size of this complex. Birefringence relaxations are well described by stretched exponential laws revealing a polydisperse distribution of hydrodynamic diameters. Comparing the size distribution of samples with different initial ratios of immunoglobuline added per magnetic nanoparticles, we evidence the graft of an antibody on particle and eventually the onset of particles aggregation. Measurements on samples separated in size by gel filtration demonstrate the robustness of our experiment for the determination of size distribution and its modification due to the adsorption of a macromolecule. The immunoglobuline binding assay is performed comparatively for ionic magnetic nanoparticles with different coatings.

Journal Article↗
PubMed2002

Anisotropy of the structure factor of magnetic fluids under a field probed by small-angle neutron scattering.

Small-angle neutron scattering is used to measure the two-dimensional diffraction pattern of a monophasic magnetic colloid, under an applied magnetic field. This dipolar system presents in zero field a fluidlike structure. It is well characterized by an interaction parameter K(0)(T) proportional to the second virial coefficient, which is here positive, expressing a repulsion of characteristic length kappa-10. Under the field a strong anisotropy is observed at the lowest q vectors. The length kappa-10 remains isotropic, but the interaction parameter K(T) becomes anisotropic due to the long-range dipolar interaction. However, the system remains stable, the interaction being repulsive in all directions. Thus we do not observe any chaining of the nanoparticles under magnetic field. On the contrary, the revealed structure of our anisotropic colloid is a lowering of the concentration fluctuations along the field while the fluidlike structure, observed without field, is roughly preserved perpendicularly to the field. It expresses a strong anisotropy of the Brownian motion of the nanoparticles in the solution under applied field.

Journal Article↗
PubMed2002

Magnetophoresis and ferromagnetic resonance of magnetically labeled cells.

We develop in this paper two methods, based on different physical concepts, to quantify the uptake of magnetic nanoparticles in biological cells. The first one, magnetophoresis, is based on the measurement of the velocity of magnetically labeled cells submitted to a magnetic field gradient. The second one quantitates the particles' electronic spin using an electron paramagnetic resonance experiment. We show a quantitative agreement between both methods for macrophagic cells. The uptake kinetics and uptake capacity are discussed for macrophagic cells and other cell lines.

Biophysics↗
PubMed1997

Biomechanical events in the time to exhaustion at maximum aerobic speed.

Recent studies reported good intra-individual reproducibility, but great inter-individual variation in a sample of elite athletes, in time to exhaustion (tlim) at the maximal aerobic speed (MAS: the lowest speed that elicits VO2max in an incremental treadmill test). The purpose of the present study was, on the one hand, to detect modifications of kinematic variables at the end of the tlim of the VO2max test and, on the other hand, to evaluate the possibility that such modifications were factors responsible for the inter-individual variability in tlim. Eleven sub-elite male runners (Age = 24 +/- 6 years; VO2max = 69.2 +/- 6.8 ml kg-1 min-1; MAS = 19.2 +/- 1.45 km h-1; tlim = 301.9 +/- 82.7 s) performed two exercise tests on a treadmill (0% slope): an incremental test to determine VO2max and MAS, and an exhaustive constant velocity test to determine tlim at MAS. Statistically significant modifications were noted in several kinematic variables. The maximal angular velocity of knee during flexion was the only variable that was both modified through the tlim test and influenced the exercise duration. A multiple correlation analysis showed that tlim was predicted by the modifications of four variables (R = 0.995, P < 0.01). These variables are directly or indirectly in relation with the energic cost of running. It was concluded that runners who demonstrated stable running styles were able to run longer during MAS test because of optimal motor efficiency.

Adaptation, Physiological↗
PubMedDate not supplied

Single-cell detection by gradient echo 9.4 T MRI: a parametric study.

Recent studies have shown that cell migration can be monitored in vivo by magnetic resonance imaging after intracellular contrast agent incorporation. This is due to the dephasing effect on proton magnetization of the local magnetic field created by a labelled cell. Anionic iron oxide nanoparticles (AMNP) are among the most efficient and non-toxic contrast agents to be spontaneously taken up by a wide variety of cells. Here we measured the iron load and magnetization of HeLa tumour cells labelled with AMNP, as a function of the external magnetic field. High-resolution gradient echo 9.4 T MRI detected individual labelled cells, whereas spin echo sequences were poorly sensitive. We then conducted a systematic study in order to determine the gradient echo sequence parameters (echo time, cell magnetization and resolution) most suitable for in vivo identification of single cells.

Cell Survival↗