A simple and widely applicable method to 59Fe-radiolabel monodisperse superparamagnetic iron oxide nanoparticles for in vivo quantification studies.

A simple, fast, efficient, and widely applicable method to radiolabel the cores of monodisperse superparamagnetic iron oxide nanoparticles (SPIOs) with (59)Fe was developed. These cores can be used as precursors for a variety of functionalized nanodevices. A quality control using filtration techniques, size-exclusion chromatography, chemical degradation methods, transmission electron microscopy, and magnetic resonance imaging showed that the nanoparticles were stably labeled with (59)Fe. Furthermore, the particle structure and the magnetic properties of the SPIOs were unchanged. In a second approach, monodisperse SPIOs stabilized with (14)C-oleic acid were synthesized, and the stability of this shell labeling was studied. In proof of principle experiments, the (59)Fe-SPIOs coated with different shells to make them water-soluble were used to evaluate and compare in vivo pharmacokinetic parameters such as blood half-life. It could also be shown that our radiolabeled SPIOs embedded in recombinant lipoproteins can be used to quantify physiological processes in closer detail than hitherto possible. In vitro and in vivo experiments showed that the (59)Fe label is stable enough to be applied in vivo, whereas the (14)C label is rapidly removed from the iron core and is not adequate for in vivo studies. To obtain meaningful results in in vivo experiments, only (59)Fe-labeled SPIOs should be used.

Brown adipose tissue activity controls triglyceride clearance.

Brown adipose tissue (BAT) burns fatty acids for heat production to defend the body against cold and has recently been shown to be present in humans. Triglyceride-rich lipoproteins (TRLs) transport lipids in the bloodstream, where the fatty acid moieties are liberated by the action of lipoprotein lipase (LPL). Peripheral organs such as muscle and adipose tissue take up the fatty acids, whereas the remaining cholesterol-rich remnant particles are cleared by the liver. Elevated plasma triglyceride concentrations and prolonged circulation of cholesterol-rich remnants, especially in diabetic dyslipidemia, are risk factors for cardiovascular disease. However, the precise biological role of BAT for TRL clearance remains unclear. Here we show that increased BAT activity induced by short-term cold exposure controls TRL metabolism in mice. Cold exposure drastically accelerated plasma clearance of triglycerides as a result of increased uptake into BAT, a process crucially dependent on local LPL activity and transmembrane receptor CD36. In pathophysiological settings, cold exposure corrected hyperlipidemia and improved deleterious effects of insulin resistance. In conclusion, BAT activity controls vascular lipoprotein homeostasis by inducing a metabolic program that boosts TRL turnover and channels lipids into BAT. Activation of BAT might be a therapeutic approach to reduce elevated triglyceride concentrations and combat obesity in humans.

Microencapsulation of inorganic nanocrystals into PLGA microsphere vaccines enables their intracellular localization in dendritic cells by electron and fluorescence microscopy.

Biodegradable poly-(D,L-lactide-co-glycolide) microspheres (PLGA-MS) are approved as a drug delivery system in humans and represent a promising antigen delivery device for immunotherapy against cancer. Immune responses following PLGA-MS vaccination require cross-presentation of encapsulated antigen by professional antigen presenting cells (APCs). While the potential of PLGA-MS as vaccine formulations is well established, the intracellular pathway of cross-presentation following phagocytosis of PLGA-MS is still under debate. A part of the controversy stems from the difficulty in unambiguously identifying PLGA-MS within cells. Here we show a novel strategy for the efficient encapsulation of inorganic nanocrystals (NCs) into PLGA-MS as a tool to study their intracellular localization. We microencapsulated NCs as an electron dense marker to study the intracellular localization of PLGA-MS by transmission electron microscopy (TEM) and as fluorescent labels for confocal laser scanning microscopy. Using this method, we found PLGA-MS to be rapidly taken up by dendritic cells and macrophages. Co-localization with the lysosomal marker LAMP1 showed a lysosomal storage of PLGA-MS for over two days after uptake, long after the initiation of cross-presentation had occurred. Our data argue against an escape of PLGA-MS from the endosome as has previously been suggested as a mechanism to facilitate cross-presentation of PLGA-MS encapsulated antigen.

A highly effective, nontoxic T1 MR contrast agent based on ultrasmall PEGylated iron oxide nanoparticles.

In this study we systematically developed a potential MR T(1) contrast agent based on very small PEGylated iron oxide nanoparticles. We adjusted the size of the crystalline core providing suitable relaxometric properties. In addition, a dense and optimized PEG coating provides high stability under physiological conditions together with low cytotoxicity and low nonspecific phagocytosis into macrophage cells as a part of the reticulo endothelial system at biologically relevant concentrations. The as developed contrast agent has the lowest r(2)/r(1) ratio (2.4) at 1.41 T reported so far for PEGylated iron oxide nanoparticles as well as a r(1) relaxivity (7.3 mM(-1) s(-1)) that is two times higher compared to that of Magnevist as a typical T(1) contrast agent based on gadolinium as a clinical standard.

Real-time magnetic resonance imaging and quantification of lipoprotein metabolism in vivo using nanocrystals.

Semiconductor quantum dots and superparamagnetic iron oxide nanocrystals have physical properties that are well suited for biomedical imaging. Previously, we have shown that iron oxide nanocrystals embedded within the lipid core of micelles show optimized characteristics for quantitative imaging. Here, we embed quantum dots and superparamagnetic iron oxide nanocrystals in the core of lipoproteins--micelles that transport lipids and other hydrophobic substances in the blood--and show that it is possible to image and quantify the kinetics of lipoprotein metabolism in vivo using fluorescence and dynamic magnetic resonance imaging. The lipoproteins were taken up by liver cells in wild-type mice and displayed defective clearance in knock-out mice lacking a lipoprotein receptor or its ligand, indicating that the nanocrystals did not influence the specificity of the metabolic process. Using this strategy it is possible to study the clearance of lipoproteins in metabolic disorders and to improve the contrast in clinical imaging.

Size and surface effects on the MRI relaxivity of manganese ferrite nanoparticle contrast agents.

Superparamagnetic MnFe2O4 nanocrystals of different sizes were synthesized in high-boiling ether solvent and transferred into water using three different approaches. First, we applied a ligand exchange in order to form a water soluble polymer shell. Second, the particles were embedded into an amphiphilic polymer shell. Third, the nanoparticles were embedded into large micelles formed by lipids. Although all approaches lead to effective negative contrast enhancement, we observed significant differences concerning the magnitude of this effect. The transverse relaxivity, in particular r2*, is greatly higher for the micellar system compared to the polymer-coated particles using same-sized nanoparticles. We also observed an increase in transverse relaxivities with increasing particle size for the polymer-coated nanocrystals. The results are qualitatively compared with theoretical models describing the dependence of relaxivity on the size of magnetic spheres.