Beyond blood brain barrier breakdown – in vivo detection of occult neuroinflammatory foci by magnetic nanoparticles in high field MRI

BACKGROUND: Gadopentate dimeglumine (Gd-DTPA) enhanced magnetic resonance imaging (MRI) is widely applied for the visualization of blood brain barrier (BBB) breakdown in multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). Recently, the potential of magnetic nanoparticles to detect macrophage infiltration by MRI was demonstrated. We here investigated a new class of very small superparamagnetic iron oxide particles (VSOP) as novel contrast medium in murine adoptive-transfer EAE. METHODS: EAE was induced in 17 mice via transfer of proteolipid protein specific T cells. MR images were obtained before and after application of Gd-DTPA and VSOP on a 7 Tesla rodent MR scanner. The enhancement pattern of the two contrast agents was compared, and correlated to histology, including Prussian Blue staining for VSOP detection and immunofluorescent staining against IBA-1 to identify macrophages/microglia. RESULTS: Both contrast media depicted BBB breakdown in 42 lesions, although differing in plaques appearances and shapes. Furthermore, 13 lesions could be exclusively visualized by VSOP. In the subsequent histological analysis, VSOP was localized to microglia/macrophages, and also diffusely dispersed within the extracellular matrix. CONCLUSION: VSOP showed a higher sensitivity in detecting BBB alterations compared to Gd-DTPA enhanced MRI, providing complementary information of macrophage/microglia activity in inflammatory plaques that has not been visualized by conventional means

Magnetic resonance imaging of neuroinflammation in a mouse model of multiple sclerosis

Die kraniale und spinale Bildgebung mittels Magnetresonanztomographie (MRT) hat in den vergangenen Jahren einen zentralen Stellenwert zur Diagnosestellung, Verlaufs- und Therapiekontrolle der Multiplen Sklerose (MS) erlangt. Jedoch besteht trotz hoher Sensitivität der kontrastmittelgestützten MRT bei der Darstellung von entzündlichen Läsionen des zentralen Nervensystems (ZNS) noch immer eine Diskrepanz zwischen den klinischen Symptomen des Patienten und den Befunden der Bildgebung, bekannt als „klinisch- radiologisches Paradox“ der MS. Zielsetzung dieser Studie war eine differenziertere Visualisierung einzelner Teilaspekte der Pathophysiologie der MS mittels MRT. Dazu wurden in einem Tiermodell für MS, der experimentellen autoimmunen Enzephalomyelitis, zwei experimentelle MRT Kontrastmittel, die paramagnetischen Nanopartikel VSOP und das Gadoliniumderivat Gadofluorin M (Gf), im Vergleich zu dem herkömmlichen Kontrastmittel Gadopentetat-Dimeglumin (Gd-DTPA) untersucht. SJL/J Mäuse wurden nach Transfer von Proteolipid- spezifischen, enzephalitogenen T-Zellen, bzw. Ovalbumin-spezifischen, ZNS- irrelevanten T-Zellen in einer Subgruppe, zu verschiedenen Zeitpunkten während des Krankheitsverlaufs mit einem 7 Tesla Kleintier MRT vor und nach Kontrastmittelgabe untersucht. Die MRT Schnittsequenzen wurden mit konventionell histologischen und immunhistochemisch gefärbten Gewebeschnitten korreliert. Beide experimentelle Kontrastmittel stellten zusätzliche Läsionen dar, die mit Gd-DTPA nicht detektiert werden konnten. Die Verteilung der Läsionen umfasste das gesamte ZNS und ähnelte dem Läsionsmuster beschrieben bei MS. Gf zeigte sich besonders geeignet für die Visualisierung entzündlicher Hirnnervenveränderungen, z.B. des Nervus opticus. Zudem wurde eine ausgeprägte Kontrastmittelanreicherung im Plexus choroideus und anderen zirkumventrikulären Organen von erkrankten Mäusen festgestellt. VSOP erwies sich ausgesprochen sensitiv in der Darstellung von Bluthirnschrankenveränderungen und fungierte gleichzeitig als zellulärer Marker für aktivierte Makrophagen/Mikroglia. Durch Anwendung von VSOP und Gf konnten verschiedene zelluläre, parenchymatöse und vaskuläre Veränderungen während einer entzündlichen Erkrankung des zentralen Nervensystems in vivo mittels MRT beobachtet werden, die der konventionellen Bildgebung bislang verborgen blieben.Magnetic resonance imaging (MRI) of the brain and the spinal cord has gained a central role for the diagnosis and paraclinical assessment of disease progression in patients suffering from multiple sclerosis (MS). However, despite high sensitivity of contrast-enhanced MRI for the visualization of inflammatory lesions within in the central nervous system (CNS), there is still a mismatch between the clinical symptoms of the patient and the burden of disease seen on MRI described as the “clinico-radiological paradox” of MS. The aim of the study was to investigate novel MRI techniques to address certain aspects of the pathophysiology of MS. Two novel MRI contrast agents, paramagnetic nanoparticles (VSOP) and gadolinium based Gadofluorine M (Gf), were investigated in experimental autoimmune encephalomyelitis (EAE), a mouse model of MS, and compared to the conventional contrast agent gadopentate- dimeglumine (Gd-DTPA). Hereby, SJL/J mice were imaged at different time points during the course of disease on a dedicated 7 Tesla rodent MRI, before and after transfer of proteolipid-protein specific encephalitogenic T-cells, or Ovalbumine-specific CNS-irrelevant T-cells respectively. MRI data were correlated with brain slices stained with immunofluoresence and conventional histological techniques. Both experimental contrast agents revealed additional contrast-enhancing lesions not detected on Gd-DTPA-enhanced images. The lesion distribution was similar to the pattern of lesions described in MS. In detail, Gf was particularly sensitive for the detection of inflammation of the cranial nerves, e.g. the optic nerve. Additionally, Gf largely enhanced in the choroid plexus and other circumventricular organs of EAE mice. VSOP detected blood- brain-barrier breakdown with high sensitivity, but was simultaneously incorporated into activated macrophages/microglia, highlighting these cells on T2*-weighted MRI. Applying VSOP and Gf-enhanced MRI, we could monitor different cellular, parenchymal and vascular alterations during CNS inflammation in vivo, which were occult for conventional MR imaging

Beyond blood brain barrier breakdown – <it>in vivo </it>detection of occult neuroinflammatory foci by magnetic nanoparticles in high field MRI

Abstract Background Gadopentate dimeglumine (Gd-DTPA) enhanced magnetic resonance imaging (MRI) is widely applied for the visualization of blood brain barrier (BBB) breakdown in multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). Recently, the potential of magnetic nanoparticles to detect macrophage infiltration by MRI was demonstrated. We here investigated a new class of very small superparamagnetic iron oxide particles (VSOP) as novel contrast medium in murine adoptive-transfer EAE. Methods EAE was induced in 17 mice via transfer of proteolipid protein specific T cells. MR images were obtained before and after application of Gd-DTPA and VSOP on a 7 Tesla rodent MR scanner. The enhancement pattern of the two contrast agents was compared, and correlated to histology, including Prussian Blue staining for VSOP detection and immunofluorescent staining against IBA-1 to identify macrophages/microglia. Results Both contrast media depicted BBB breakdown in 42 lesions, although differing in plaques appearances and shapes. Furthermore, 13 lesions could be exclusively visualized by VSOP. In the subsequent histological analysis, VSOP was localized to microglia/macrophages, and also diffusely dispersed within the extracellular matrix. Conclusion VSOP showed a higher sensitivity in detecting BBB alterations compared to Gd-DTPA enhanced MRI, providing complementary information of macrophage/microglia activity in inflammatory plaques that has not been visualized by conventional means.</p