ISSN 1916-5382

http://gsjournal.net/

The General Science Journal (2013) 1-8

Magnetic nanoparticles as contrast agents for magnetic resonance imaging Š. Durdík,1,2 M. Babincová,3 K. Kontrišová1, C. Bergemann,4 P. Babinec3,* 1

St. Elizabeth Cancer Institute, Heydukova 10, 812 50 Bratislava, Slovakia

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Department of Oncological Surgery, Faculty of Medicine, Comenius University, Špitálska

24, 813 72 Bratislava, Slovakia 3

Department of Nuclear Physics and Biophysics, Comenius University, Mlynská dolina F1,

842 48 Bratislava, Slovakia 4

Chemicell GmbH, Eressburg Straße 22-23, 12103 Berlin, Germany

* Corresponding author: email: [email protected]

ABSTRACT: We have analyzed 15 different magnetic nanoparticles as possible contrast agents for magnetic resonance imaging. A gradient echo (GEFI) and a multi-slice MRI protocol with a Rapid Acquisition with Relaxation Enhancement (RARE) sequence were used. Of particular importance is exceptional suitability of polyMAG nanoparticles, as a MRI contrast agent. This positively charged nanoparticle is readily endocytosed by cells, and this efficiency is further enhanced by action of magnetic field, therefore it is for a relatively long time used as a basic reagent for magnetofection.

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Introduction Multifunctionalmagnetic nanoparticles [1-4] have a diverse potential applications in many biological and medical applications such as cell separation [5,6], drug targeting [7-9], electromagnetic hyperthermia [10], or magnetic resonance contrast enhancement [11]. Magnetic nanoparticle-based gene transfection (magnetofection™) has also been shown to be effective in combination with both viral vectors and with non-viral agents [12-15]. A number of techniques have been developed to track the migration of T cells in animal models, including the histological examination of tissue sections by light or confocal laser microscopy, intravital microscopy, whole organ or body scintigraphy, and two photon microscopy. However, these methods suffer various shortcomings, including the examination of selected organs rather than the organism as a whole, and the inability to perform longitudinal studies. A number of whole-animal approaches have therefore been developed to allow non-invasive, repetitive monitoring of T cell migration, including bioluminescence (BLI) imaging, micro-positron emission tomography (PET), single-photon emission computed (SPECT) tomography, and magnetic resonance (MR) imaging. While highly sensitive, BLI, PET and SPECT are limited by relatively poor spatial resolution, short label half-lives, limited tissue penetration (BLI) and the application of ionizing radiation (PET; SPECT). Achieving high-resolution images with MRI — to the level of tens of microns — can require long acquisition times. This is a significant limitation for in vivo studies, particularly when small quantities of contrast agent are present in the target tissue. Much of the published literature on imaging the transmigration of T cells from the vascular compartment has therefore used MR microscopy, in which the subject is perfusion fixed and whole body imaging, or organ imaging ex vivo, is performed using acquisition times of several hours. While this strategy achieves the desired resolution, it precludes dynamic longitudinal studies. An alternative approach that allows serial MR imaging is to optimize contrast by the local or intraperitoneal injection of labelled T cells. In our study, we have employed various superparamagnetic iron oxide nanoparticles and microparticlers as a T2 contrast agent for suitable for imaging CD4+ stem cells.

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Materials and Methods The MRI recordings are performed using 2.95 T scanner was a MEDSPEC-DBX whole body tomograph (Bruker, Ettlingen, Germany) equipped with a 200 mT/m microimaging gradient system and a 45 mm inner diameter resonator. Two MR sequences were used. A gradient echo (GEFI) and a multi-slice MRI protocol with a Rapid Acquisition with Relaxation Enhancement (RARE) sequence were used. The following MR parameters were used. Acquisition matrix 256×128 and reconstructed 256×256, slice thickness 800 µm, field of view 4 cm. Specifically for the GEFI sequence TR 144.2 ms, TE 10.0 ms, averages 16 and for the RARE sequence recovery time 2095 ms, time between refocusing pulses and phase encoding gradient incrementation to yield an effective echo time TE 46.2 ms, averages 8, rare factor 16. When spinning magnet of Fe3O4 nanoparticles was placed in a strong magnetic field, it started processing around it just as a spinning top processes about the vertical axis before falling. The fluid agar gel was detected by making the hydrogen nuclei present in the water molecules under strong magnetic field. The intensity difference of energy radiation between fluid in gel and injected superparamagnetic Fe3O4 nanoparticles was shown by different darkness in images. A gradient echo (GEFI) sequence that is more sensitive to the susceptibility changes caused by the superparamagnetic iron particles and will qualitatively show the presence of the nanoparticles. The distributions of the particles were characterized using a multi-slice MRI protocol with a Rapid Acquisition with Relaxation Enhancement (RARE) sequence.

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Results and Discussion Table 1: Various magnetic nanoparticles suspended in 1.2 % agar gel as potential MRI contrast agents GEFI Sample Characterization RARE sequence 1. MG-D/AM

2. MAG-25/2

3. bead MAG

4. bead MAG11/8

Aqueous dispersion of magnetic nanoparticles with a diameter of 50 nm, covered with a hydrophilic matrix of crosslinked starch with terminal cationexchange phosphate groups. Chemicell GmbH. Aqueous dispersion of magnetic nanoparticles with a diameter of 100 nm, covered with a hydrophilic matrix of crosslinked starch with terminal cationexchange phosphate groups. Chemicell GmbH. Magnetic microparticles with a diameter of 1 µm, covered with a hydrophilic matrix of crosslinked starch with terminal cationexchange phosphate groups. Chemicell GmbH. Magnetic microparticles with a diameter of 1 µm, covered with a hydrophilic matrix of crosslinked starch with terminal cationexchange phosphate groups. Chemicell GmbH.

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5. trans MAG-C

Starch modified 50 nm magnetic nanoparticles used also for magnetic cell transfection. Chemicell GmbH.

7. MAG-D6/NK

Starch modified 50 nm magnetic nanoparticles. Chemicell GmbH.

8. polyMAG

Aqueous dispersion of magnetic nanoparticles with a diameter of 340 nm, covered with a polyethylenimine for magnetic transfection of cells. Chemicell GmbH and OZ-Biosciences.

9. Magnetic microbubbles + DOX 5ul on Petri dish

Perfluorocarbom microbubbles with dimension ~ 10 µm with encapsulated magnetite nanoparticles, (prepared by C. Plank, TU Munich).

10. Magnetic microbubbles 5ul on Petri dish

Perfluorocarbon microbubbles with dimension ~ 10 µm with encapsulated magnetite nanoparticles and doxorubicin (prepared by C. Plank, TU Munich).

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12.MAG/PEG/Dip hosphate

PEGdiphosphate covered long circulating magnetic nanoparticles, size 80 nm. Chemicell GmbH.

14.MAG-CT

Magnetic particles with a diameter of 0.1 µm with sodium citrate functional group for MRI. Chemicell GmbH.

15.MAG-HS

Starch modified 50 nm magnetic nanoparticles. Chemicell GmbH.

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Of particular importance is exceptional suitability of polyMAG nanoparticles (sample 8), as a MRI contrast agent which we have already used in our (cancer) cell labeling studies. This positively charged nanoparticle is readily endocytosed by cells, and this efficiency is further enhanced by action of magnetic field, morevover it is for a relatively long time used as a basic reagent for magnetofection.

Acknowledgements This work was supported by VEGA grant 1/0642/11. We are grateful Dr. V. Altanerová, Prof. C. Altaner, Dr. P. Szomolanyi, and Prof. C. Plank for their kind help in experiments.

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