Maria Engström

Polyethylene glycol-covered ultra-small Gd2O3 nanoparticles for positive contrast at 1.5 T magnetic resonance clinical scanning

The size distribution and magnetic properties of ultra-small gadolinium oxide crystals (US-Gd2O3) were studied, and the impact of polyethylene glycol capping on the relaxivity constants (r1, r2) an ...

Synthesis and Characterization of PEGylated Gd2O3 Nanoparticles for MRI Contrast Enhancement

Recently, much attention has been given to the development of biofunctionalized nanoparticles with magnetic properties for novel biomedical imaging. Guided, smart, targeting nanoparticulate magnetic resonance imaging (MRI) contrast agents inducing high MRI signal will be valuable tools for future tissue specific imaging and investigation of molecular and cellular events. In this study, we report a new design of functionalized ultrasmall rare earth based nanoparticles to be used as a positive contrast agent in MRI. The relaxivity is compared to commercially available Gd based chelates. The synthesis, PEGylation, and dialysis of small (3-5 nm) gadolinium oxide (DEG-Gd(2)O(3)) nanoparticles are presented. The chemical and physical properties of the nanomaterial were investigated with Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and dynamic light scattering. Neutrophil activation after exposure to this nanomaterial was studied by means of fluorescence microscopy. The proton relaxation times as a function of dialysis time and functionalization were measured at 1.5 T. A capping procedure introducing stabilizing properties was designed and verified, and the dialysis effects were evaluated. A higher proton relaxivity was obtained for as-synthesized diethylene glycol (DEG)-Gd(2)O(3) nanoparticles compared to commercial Gd-DTPA. A slight decrease of the relaxivity for as-synthesized DEG-Gd(2)O(3) nanoparticles as a function of dialysis time was observed. The results for functionalized nanoparticles showed a considerable relaxivity increase for particles dialyzed extensively with r(1) and r(2) values approximately 4 times the corresponding values for Gd-DTPA. The microscopy study showed that PEGylated nanoparticles do not activate neutrophils in contrast to uncapped Gd(2)O(3). Finally, the nanoparticles are equipped with Rhodamine to show that our PEGylated nanoparticles are available for further coupling chemistry, and thus prepared for targeting purposes. The long term goal is to design a powerful, directed contrast agent for MRI examinations with specific targeting possibilities and with properties inducing local contrast, that is, an extremely high MR signal at the cellular and molecular level.

Positive MRI Enhancement in THP-1 Cells with Gd2O3 Nanoparticles

There is a demand for more efficient and tissue-specific MRI contrast agents and recent developments involve the design of substances useful as molecular markers and magnetic tracers. In this study, nanoparticles of gadolinium oxide (Gd2O3) have been investigated for cell labeling and capacity to generate a positive contrast. THP-1, a monocytic cell line that is phagocytic, was used and results were compared with relaxivity of particles in cell culture medium (RPMI 1640). The results showed that Gd2O3-labeled cells have shorter T1 and T2 relaxation times compared with untreated cells. A prominent difference in signal intensity was observed, indicating that Gd2O3 nanoparticles can be used as a positive contrast agent for cell labeling. The r1 for cell samples was 4.1 and 3.6 s(-1) mm(-1) for cell culture medium. The r2 was 17.4 and 12.9 s(-1) mm(-1), respectively. For r1, there was no significant difference in relaxivity between particles in cells compared to particles in cell culture medium, (p(r1) = 0.36), but r2 was significantly different for the two different series (p(r2) = 0.02). Viability results indicate that THP-1 cells endure treatment with Gd2O3 nanoparticles for an extended period of time and it is therefore concluded that results in this study are based on viable cells.

Inactivation of the forkhead transcription factor FoxO3 is essential for PKB-mediated survival of hematopoietic progenitor cells by kit ligand.

OBJECTIVE Kit ligand (KL) is a major survival factor for hematopoietic stem cells. Although anti-apoptotic bcl-2 family members are expressed in these cells, the survival effects by KL appear to involve other mechanisms. Survival signals can also be elicited by the activation of phosphatidylinositol 3-kinase (PI3K) and protein kinase B (PKB), which in turn inactivates forkhead transcription factors, known to be potent regulators of apoptosis. In this study, we investigated the involvement of PKB, FoxO1, FoxO3, and FoxO4 in c-kit-mediated survival. METHODS By Western blot analysis, immunofluorescence, and subcellular fractionation, we analyzed the effects of KL on PKB and different forkhead family members in two factor-dependent cell lines, FDCP-mix and FDC-P1, as well as primary mouse bone marrow-derived Lin(-) progenitors. Forced overexpression of triple mutated form of FoxO3 by retroviral gene transfer has enabled us to directly study its involvement in these cells. RESULTS Upon KL stimulation, PKB and its downstream target FoxO3, and to some extent FoxO1, were rapidly phosphorylated. This led to an exclusion of endogenous FoxO3 from the nucleus, which was shown to be dependent of PI3K activation. Overexpression of triple-mutated FoxO3 in a factor-dependent cell line induced apoptosis in the presence of KL. Also, triple-mutated FoxO3 was able to inhibit the colony formation of Lin(-) progenitors in KL. CONCLUSION Our data suggest that FoxO3 plays an important role in KL-mediated survival of hematopoietic progenitors. Because forkhead proteins are involved in controlling apoptosis and cell-cycle progression, this may be one important mechanism by which survival of hematopoietic progenitors is mediated.

Phosphatidylinositol 3-kinase is essential for kit ligand-mediated survival, whereas interleukin-3 and flt3 ligand induce expression of antiapoptotic Bcl-2 family genes.

Cytokines such as interleukin 3 (IL‐3), kit ligand (KL), and flt3 ligand (FL) promote survival of hematopoietic stem cells and myeloid progenitor cells. In many cell types, members of the Bcl‐2 gene family are major regulators of survival, but the mediating mechanisms are not fully understood. Using two myeloid progenitor cell lines, FDCP‐mix and FDC‐P1, as well as primary mouse bone marrow progenitors, we demonstrate that KL‐mediated survival is dependent on the activation of phosphatidylinositol‐3 (PI‐3) kinase. The inhibitor LY294002 was able to completely abolish survival mediated by KL, whereas IL‐3 and FL were only partially affected. Although all three cytokines induced phosphorylation of protein kinase B (PKB), only KL required PI‐3 kinase activity to elicit survival in hematopoietic progenitors. In contrast, pretreatment of cells with inhibitors to the MAP kinase pathway did not affect the survival. We next established if IL‐3 and FL activated antiapoptotic Bcl‐2 and the related genes Bcl‐XL and Mcl‐1. By RNA protection assay and Western blot analysis, we show that all three genes are induced by IL‐3, whereas FL induces Bcl‐2 and to some extent Bcl‐XL. Importantly, KL could not sustain their expression. Moreover, use of inhibitors implied that IL‐3 was mainly exerting its effect on Bcl‐2 at the level of transcription. The addition of LY294002 did not affect the expression of Bcl‐2 and Bcl‐XL, and thus, we conclude that expression of antiapoptotic Bcl‐2 family member genes is not dependent on PI‐3 kinase activity. Our results indicate that cytokines exert distinct survival effects and that FL and IL‐3 are capable of sustaining progenitor survival by up‐regulating the expression of Bcl‐2 and related genes.

Highly Water‐Dispersible Surface‐Modified Gd2O3 Nanoparticles for Potential Dual‐Modal Bioimaging

Water-dispersible and luminescent gadolinium oxide (GO) nanoparticles (NPs) were designed and synthesized for potential dual-modal biological imaging. They were obtained by capping gadolinium oxide nanoparticles with a fluorescent glycol-based conjugated carboxylate (HL). The obtained nanoparticles (GO-L) show long-term colloidal stability and intense blue fluorescence. In addition, L can sensitize the luminescence of europium(III) through the so-called antenna effect. Thus, to extend the spectral ranges of emission, europium was introduced into L-modified gadolinium oxide nanoparticles. The obtained EuIII-doped particles (Eu:GO-L) can provide visible red emission, which is more intensive than that without L capping. The average diameter of the monodisperse modified oxide cores is about 4 nm. The average hydrodynamic diameter of the L-modified nanoparticles was estimated to be about 13 nm. The nanoparticles show effective longitudinal water proton relaxivity. The relaxivity values obtained for GO-L and Eu:GO-L were r1=6.4 and 6.3 s−1 mM−1 with r2/r1 ratios close to unity at 1.4 T. Longitudinal proton relaxivities of these nanoparticles are higher than those of positive contrast agents based on gadolinium complexes such as Gd-DOTA, which are commonly used for clinical magnetic resonance imaging. Moreover, these particles are suitable for cellular imaging and show good biocompatibility.

Visual grading of 2D and 3D functional MRI compared with image-based descriptive measures

ObjectiveA prerequisite for successful clinical use of functional magnetic resonance imaging (fMRI) is the selection of an appropriate imaging sequence. The aim of this study was to compare 2D and 3D fMRI sequences using different image quality assessment methods. MethodsDescriptive image measures, such as activation volume and temporal signal-to-noise ratio (TSNR), were compared with results from visual grading characteristics (VGC) analysis of the fMRI results.ResultsSignificant differences in activation volume and TSNR were not directly reflected by differences in VGC scores. The results suggest that better performance on descriptive image measures is not always an indicator of improved diagnostic quality of the fMRI results.ConclusionIn addition to descriptive image measures, it is important to include measures of diagnostic quality when comparing different fMRI data acquisition methods.

IBS Patients With Normal Visceral Sensitivity Differ From Healthy Controls During the Expectation but Not the Delivery of an Aversive Distension

IBS Patients With Normal Visceral Sensitivity Differ From HealthyControls During the Expectation but Not the Delivery of an Aversive Distension