A physiological barrier distal to the anatomic blood-brain barrier in a model of transvascular delivery.
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BACKGROUND AND PURPOSE: Osmotic disruption of the blood-brain barrier (BBB) provides a method for transvascular delivery of therapeutic agents to the brain. The apparent global delivery of viral-sized iron oxide particles to the rat brain after BBB opening as seen on MR images was compared with the cellular and subcellular location and distribution of the particles. METHODS: Two dextran-coated superparamagnetic monocrystalline iron oxide nanoparticle contrast agents, MION and Feridex, were administered intraarterially in rats at 10 mg Fe/kg immediately after osmotic opening of the BBB with hyperosmolar mannitol. After 2 to 24 hours, iron distribution in the brain was evaluated first with MR imaging then by histochemical analysis and electron microscopy to assess perivascular and intracellular distribution. RESULTS: After BBB opening, MR images showed enhancement throughout the disrupted hemisphere for both Feridex and MION. Feridex histochemical staining was found in capillaries of the disrupted hemisphere. Electron microscopy showed that the Feridex particles passed the capillary endothelial cells but did not cross beyond the basement membrane. In contrast, after MION delivery, iron histochemistry was detected within cell bodies in the disrupted hemisphere, and the electron-dense MION core was detected intracellularly and extracellularly in the neuropil. CONCLUSION: MR images showing homogeneous delivery to the brain at the macroscopic level did not indicate delivery at the microscopic level. These data support the presence of a physiological barrier at the basal lamina, analogous to the podocyte in the kidney, distal to the anatomic (tight junction) BBB, which may limit the distribution of some proteins and viral particles after transvascular delivery to the brain. (+info)
Comparison of ultrasmall particles of iron oxide (USPIO)-enhanced T2-weighted, conventional T2-weighted, and gadolinium-enhanced T1-weighted MR images in rats with experimental autoimmune encephalomyelitis.
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BACKGROUND AND PURPOSE: Ultrasmall particles of iron oxide (USPIO) constitute a contrast agent that accumulates in cells from the mononuclear phagocytic system. In the CNS they may accumulate in phagocytic cells such as macrophages. The goal of this study was to compare USPIO-enhanced MR images with conventional T2-weighted images and gadolinium-enhanced T1-weighted images in a model of experimental autoimmune encephalomyelitis (EAE). METHODS: Nine rats with EAE and four control rats were imaged at 4.7 T and 1.5 T with conventional T1- and T2-weighted sequences, gadolinium-enhanced T1-weighted sequences, and T2-weighted sequences obtained 24 hours after intravenous injection of a USPIO contrast agent, AMI-227. Histologic examination was performed with hematoxylin-eosin stain, Perls' stain for iron, and ED1 immunohistochemistry for macrophages. RESULTS: USPIO-enhanced images showed a high sensitivity (8/9) for detecting EAE lesions, whereas poor sensitivity was obtained with T2-weighted images (1/9) and gadolinium-enhanced T1-weighted images (0/9). All the MR findings in the control rats were negative. Histologic examination revealed the presence of macrophages at the site where abnormalities were seen on USPIO-enhanced images. CONCLUSION: The high sensitivity of USPIO for macrophage activity relative to other imaging techniques is explained by the histologic findings of numerous perivascular cell infiltrates, including macrophages, in EAE. This work supports the possibility of intracellular USPIO transport to the CNS by monocytes/macrophages, which may have future implications for imaging of human inflammatory diseases. (+info)
Iron reductase for magnetite synthesis in the magnetotactic bacterium Magnetospirillum magnetotacticum.
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Ferric iron reductase was purified from magnetotactic bacterium Magnetospirillum (formerly Aquaspirillum) magnetotacticum (ATCC 31632) to an electrophoretically homogeneous state. The enzyme was loosely bound on the cytoplasmic face of the cytoplasmic membrane and was found more frequently in magnetic cells than in nonmagnetic cells. The molecular mass of the purified enzyme was calculated upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis to be about 36 kDa, almost the same as that calibrated by gel filtration analysis. The enzyme required NADH and flavin mononucleotide (FMN) as optimal electron donor and cofactor, respectively, and the activity was strongly inhibited by Zn2+ acting as a partial mixed-type inhibitor. The Km values for NADH and FMN were 4.3 and 0. 035 microM, respectively, and the Ki values for Zn2+ were 19.2 and 23.9 microM for NADH and FMN, respectively. When the bacterium was grown in the presence of ZnSO4, the magnetosome number in the cells and the ferric iron reductase activity declined in parallel with an increase in the ZnSO4 concentration of the medium, suggesting that the ferric iron reductase purified in the present study may participate in magnetite synthesis. (+info)
Magnetometric evaluation for the effect of chrysotile on alveolar macrophages.
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Alveolar macrophages are thought to play an important role in fibrogenesis due to asbestos exposure. In this experiment, we evaluated the effect mainly by unique magnetometry and also by conventional methods such as lactate dehydrogenase (LDH) activity measurement and morphological observations. Alveolar macrophages obtained from Syrian golden hamsters by bronchoalveolar lavages were exposed 18 hours in vitro to Fe3O4 as an indicator for magnetometry and chrysotile for experiments. A rapid decrease of the remanent magnetic field, so called "relaxation", was observed after the cessation of an external magnetic field in macrophages phagocytizing Fe3O4 alone, while relaxation was delayed in those concurrently exposed to chrysotile. Since relaxation is thought due to the cytoskeleton-driven random rotation of phagosomes containing iron oxide particles, chrysotile is considered to interfere with the cytoskeletal function of macrophages. Release of LDH from chrysotile-exposed macrophages into the medium was recognized, but it was not significantly higher than the controls. Apoptosis was negligible in macrophages exposed to chrysotile by the DNA ladder detection, the terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling method and morphological observations. Electron microscopical examinations revealed early necrotic changes in macrophages exposed to chrysotile. These findings indicate that cell magnetometry detects impaired cytoskeletal function due to in vitro exposure to chrysotile. (+info)
Neurotransplantation of magnetically labeled oligodendrocyte progenitors: magnetic resonance tracking of cell migration and myelination.
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Demyelination is a common pathological finding in human neurological diseases and frequently persists as a result of failure of endogenous repair. Transplanted oligodendrocytes and their precursor cells can (re)myelinate axons, raising the possibility of therapeutic intervention. The migratory capacity of transplanted cells is of key importance in determining the extent of (re)myelination and can, at present, be evaluated only by using invasive and irreversible procedures. We have exploited the transferrin receptor as an efficient intracellular delivery device for magnetic nanoparticles, and transplanted tagged oligodendrocyte progenitor cells into the spinal cord of myelin-deficient rats. Cell migration could be easily detected by using three-dimensional magnetic resonance microscopy, with a close correlation between the areas of contrast enhancement and the achieved extent of myelination. The present results demonstrate that magnetic resonance tracking of transplanted oligodendrocyte progenitors is feasible; this technique has the potential to be easily extended to other neurotransplantation studies involving different precursor cell types. (+info)
Magnetic resonance imaging of atherosclerotic plaque with ultrasmall superparamagnetic particles of iron oxide in hyperlipidemic rabbits.
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BACKGROUND: Based on the observation that ultrasmall superparamagnetic particles of iron oxides (USPIOs) are phagocytosed by cells of the mononuclear phagocytic system, the purpose of this study was to evaluate their use as a marker of atherosclerosis-associated inflammatory changes in the vessel wall before luminal narrowing is present. METHODS AND RESULTS: Experiments were conducted on 6 heritable hyperlipidemic and 3 New Zealand White rabbits. 3D MR angiography (MRA) of the thoracic aorta was performed on all rabbits by use of a conventional paramagnetic contrast agent that failed to reveal any abnormalities. One week later, all rabbits except 1 of the hyperlipidemic animals were injected with a USPIO contrast agent (Sinerem, Guerbet) at a dose of 1 mmol Fe/kg. 3D MRA data sets collected over the subsequent 5 days showed increasing signal in the aortic lumen. Whereas the aortic wall of the control rabbits remained smooth and bright, marked susceptibility effects became evident on day 4 within the aortic walls of hyperlipidemic rabbits. Ex vivo imaging of aortic specimens confirmed the in vivo results. Histopathology documented marked Fe uptake in macrophages embedded in atherosclerotic plaque of the hyperlipidemic rabbits. Electron microscopy showed multiple cytoplasmic Fe particles in macrophages. No such changes were seen in control rabbits or in the hyperlipidemic rabbit that had not received Sinerem. CONCLUSIONS: USPIOs are phagocytosed by macrophages in atherosclerotic plaques of the aortic wall of hyperlipidemic rabbits in a quantity sufficient to cause susceptibility effects detectable by MRI. (+info)
Monocrystalline iron oxide nanoparticles: possible solution to the problem of surgically induced intracranial contrast enhancement in intraoperative MR imaging.
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BACKGROUND AND PURPOSE: Intraoperative MR imaging is increasingly being used to control the extent of surgical resection; however, surgical manipulation itself causes intracranial contrast enhancement, which is a source of error. Our purpose was to investigate the potential of monocrystalline iron oxide nanoparticles (MIONs) to solve this problem in an animal model. METHODS: In male Wistar rats, surgical lesions of the brain were produced. The animals underwent MR examination immediately afterward. In the first group, a paramagnetic contrast agent was administered, whereas the second group of animals received MIONs 1 day before surgery. In a third group of animals, malignant glioma cells were stereotactically implanted in the caudoputamen. Two weeks later, MIONs were IV injected and the tumor was (partially) resected. Immediately after resection, MR examination was performed to determine the extent of residual tumor. RESULTS: Surgically induced intracranial contrast enhancement was seen in all animals in which a paramagnetic contrast agent was used. Conversely, when MIONs had been injected, no signal changes that could be confused with residual tumor were detected. In the animals that had undergone (partial) resection of experimental gliomas, MR assessment of residual tumor was possible without any interfering surgically induced phenomena. CONCLUSION: Because MIONs are stored in malignant brain tumor cells longer than they circulate in the blood, their use offers a promising strategy to avoid surgically induced intracranial contrast enhancement, which is known to be a potential source of error in intraoperative MR imaging. (+info)
Truncated hexa-octahedral magnetite crystals in ALH84001: presumptive biosignatures.
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McKay et al. [(1996) Science 273, 924-930] suggested that carbonate globules in the meteorite ALH84001 contained the fossil remains of Martian microbes. We have characterized a subpopulation of magnetite (Fe(3)O(4)) crystals present in abundance within the Fe-rich rims of these carbonate globules. We find these Martian magnetites to be both chemically and physically identical to terrestrial, biogenically precipitated, intracellular magnetites produced by magnetotactic bacteria strain MV-1. Specifically, both magnetite populations are single-domain and chemically pure, and exhibit a unique crystal habit we describe as truncated hexa-octahedral. There are no known reports of inorganic processes to explain the observation of truncated hexa-octahedral magnetites in a terrestrial sample. In bacteria strain MV-1 their presence is therefore likely a product of Natural Selection. Unless there is an unknown and unexplained inorganic process on Mars that is conspicuously absent on the Earth and forms truncated hexa-octahedral magnetites, we suggest that these magnetite crystals in the Martian meteorite ALH84001 were likely produced by a biogenic process. As such, these crystals are interpreted as Martian magnetofossils and constitute evidence of the oldest life yet found. (+info)