Fluorescent Bacterial Magnetic Nanoparticles as Bimodal Contrast Agents

Objectives:The purpose of this study was to assess whether fluorochrome-coupled bacterial magnetic nanoparticles can be used as bimodal contrast agent for both magnetic resonance imaging (MRI) and near-infrared fluorescence optical (NIRF) imaging of cultured macrophages. Materials and Methods:Bacterial magnetic nanoparticles (magnetosomes, particle diameter: 42 nm) were harvested from Magnetospirillum gryphiswaldense and characterized by using MRI. After covalent coupling to the fluorescent dye DY-676 (λabs./λem.= 676 nm/701 nm, Dyomics, Jena, Germany), the fluorescent magnetosomes were analyzed by fluorescence-activated cell sorting. Subsequently, murine macrophages J774 were incubated with the bimodal contrast agent (3 hours) and examined by a whole-body near infrared small animal imaging system as well as by using a 1.5 T clinical MR system. Moreover, labeled cells were characterized using confocal laser scanning microscopy (CLSM) and ultrathin section transmission electron microscopy. Results:Characterization of the nanoparticles by MRI revealed R1 and R2 relaxivities of 3.2 mM−1s−1 and 526 mM−1s−1, respectively. Fluorochrome-coupled magnetosomes exhibited increased fluorescence intensities at wavelengths >670 nm. Macrophages that were incubated with the contrast agent showed a significant fluorescence emission in the near infrared range as imaged with a whole body NIR imaging system, FACS analysis and CLSM. Moreover, CLSM data showed the greatest fluorescence intensities within intracellular compartments and colocalized with the magnetosomes. With MRI, both T1 and T2 relaxation times were substantially shortened at concentrations greater than 600 cells/&mgr;L. Discussion and Conclusion:Macrophages could be labeled with fluorescent magnetosomes, and they were successfully imaged using both a 1.5 T MR scanner as well as with NIRF optical methods. The use of this bimodal contrast agent for diagnostic purposes may benefit from the excellent spatial resolution of the MRI and the high sensitivity of the fluorescence imaging.

[1]  H. Kauczor,et al.  Gadofluorine M Uptake in Stem Cells as a New Magnetic Resonance Imaging Tracking Method: An In Vitro and In Vivo Study , 2006, Investigative radiology.

[2]  Z. Fayad,et al.  Clearance of Iron Oxide Particles in Rat Liver: Effect of Hydrated Particle Size and Coating Material on Liver Metabolism , 2006, Investigative radiology.

[3]  Damien Faivre,et al.  An acidic protein aligns magnetosomes along a filamentous structure in magnetotactic bacteria , 2006, Nature.

[4]  J. Frank,et al.  Gadolinium-Fullerenol as a Paramagnetic Contrast Agent for Cellular Imaging , 2006, Investigative radiology.

[5]  Klaas Nicolay,et al.  Quantum dots with a paramagnetic coating as a bimodal molecular imaging probe. , 2006, Nano letters.

[6]  Ajay Kumar Gupta,et al.  Synthesis and surface engineering of iron oxide nanoparticles for biomedical applications. , 2005, Biomaterials.

[7]  Eugenio Picano,et al.  Economic and biological costs of cardiac imaging , 2005, Cardiovascular ultrasound.

[8]  W. Heindel,et al.  Cell tagging with clinically approved iron oxides: feasibility and effect of lipofection, particle size, and surface coating on labeling efficiency. , 2005, Radiology.

[9]  Vasilis Ntziachristos,et al.  Looking and listening to light: the evolution of whole-body photonic imaging , 2005, Nature Biotechnology.

[10]  Ernst J. Rummeny,et al.  Capacity of human monocytes to phagocytose approved iron oxide MR contrast agents in vitro , 2004, European Radiology.

[11]  Sanjiv Sam Gambhir,et al.  Molecular imaging applications for immunology. , 2004, Clinical immunology.

[12]  W. Kaiser,et al.  Near-infrared fluorescence imaging of HER-2 protein over-expression in tumour cells , 2004, European Radiology.

[13]  D. Schüler,et al.  Biochemical and Proteomic Analysis of the Magnetosome Membrane in Magnetospirillum gryphiswaldense , 2004, Applied and Environmental Microbiology.

[14]  Heather Kalish,et al.  Comparison of Transfection Agents in Forming Complexes with Ferumoxides, Cell Labeling Efficiency, and Cellular Viability , 2004, Molecular imaging.

[15]  David W Townsend,et al.  PET/CT today and tomorrow. , 2004, Journal of nuclear medicine : official publication, Society of Nuclear Medicine.

[16]  Ralph Weissleder,et al.  A multimodal nanoparticle for preoperative magnetic resonance imaging and intraoperative optical brain tumor delineation. , 2003, Cancer research.

[17]  J. Debatin,et al.  [Magnetosomes as biological model for iron binding: relaxivity determination with MRI]. , 2003, RoFo : Fortschritte auf dem Gebiete der Rontgenstrahlen und der Nuklearmedizin.

[18]  J Bittoun,et al.  Cell internalization of anionic maghemite nanoparticles: Quantitative effect on magnetic resonance imaging , 2003, Magnetic resonance in medicine.

[19]  S. Gambhir,et al.  Molecular imaging in living subjects: seeing fundamental biological processes in a new light. , 2003, Genes & development.

[20]  U. Heyen,et al.  Growth and magnetosome formation by microaerophilic Magnetospirillum strains in an oxygen-controlled fermentor , 2003, Applied Microbiology and Biotechnology.

[21]  P. Reimer,et al.  Ferucarbotran (Resovist): a new clinically approved RES-specific contrast agent for contrast-enhanced MRI of the liver: properties, clinical development, and applications , 2003, European Radiology.

[22]  Paul K Marsden,et al.  Simultaneous PET and NMR. , 2002, The British journal of radiology.

[23]  Ralph Weissleder,et al.  Annexin V–CLIO: A Nanoparticle for Detecting Apoptosis by MRI , 2002, Molecular imaging.

[24]  Hakho Lee,et al.  Microelectromagnets for the control of magnetic nanoparticles , 2001 .

[25]  V. Ntziachristos,et al.  Fortschritte in der optischen Bildgebung , 2001, Der Radiologe.

[26]  R. Weissleder,et al.  [Progress in optical imaging]. , 2001, Der Radiologe.

[27]  H. Biersack,et al.  FDG PET and immunoscintigraphy with 99mTc-labeled antibody fragments for detection of the recurrence of colorectal carcinoma. , 2000, Journal of nuclear medicine : official publication, Society of Nuclear Medicine.

[28]  M D Blaufox,et al.  PET imaging in oncology. , 2000, Seminars in nuclear medicine.

[29]  R J Jaszczak,et al.  Single photon emission computed tomography (SPECT). Part II: Clinical applications. , 1986, Investigative radiology.