Geun Ho Im

Hollow Manganese Oxide Nanoparticles as Multifunctional Agents for Magnetic Resonance Imaging and Drug Delivery

Nanometer-sized colloidal particles with small size and large surface area have many superior properties when used as magnetic resonance imaging (MRI) contrast agents, such as their ability to carry large payloads of active magnetic centers, easy penetration of biological membranes, long blood circulation times, and efficient conjugation to affinity molecules. Thus, they have the potential to allow us to visualize targets at low imaging-agent concentration with high sensitivity and sepcificity. Furthermore, nanoparticles can be used in combination with therapeutic agents as bifunctional medical systems that enable simultaneous MRI diagnosis and drug treatment. For example, superparamagnetic iron oxide nanoparticles have been developed as efficient T2 contrast agents and employed to image tumors, stem cell migration, and cancer metastases. Some colloidal nanoparticles containing gadolinium(III) or manganese(II) have recently been reported as potent T1 MRI contrast agents. [4] Very recently, some of the present authors developed MnO nanoparticles as T1 contrast agents for MRI signal enhancement of the anatomic brain structure. The further development of nanoparticle MRI contrast agents will require materials with higher relaxivity than the current state of the art that can operate at much lower concentrations of potentially toxic metal ions such as Gd and Mn. In this context, hollow nanoparticles with interior void spaces are attractive candidates owing to their large water-accessible surface areas, which are able to carry high payloads of MR-active magnetic centers, and because they can take up a large amount of therapeutic drug within the interior void. While hollow nanoparticles containing magnetic ions have recently been prepared through several synthetic strategies, there are few examples of the investigation of their medical applications. Herein, we report a novel and facile synthesis of hollow manganese oxide nanoparticles (HMONs) and their potential application as multifunctional agents for simultaneous MR imaging and drug delivery. We demonstrate the greatly improved relaxivities of the hollow nanoparticles along with their efficient cellular uptake and drug loading capacities. These properties allow us to develop these particles for the delivery of therapeutic drugs as well as for diagnostic imaging. Manganese oxide nanoparticles with a diameter of 20 nm stabilized by oleic acid (MONs) as well as water-dispersible manganese oxide nanoparticles (WMONs) were prepared using a reported procedure involving the thermal decomposition of a manganese oleate complex and encapsulation with poly(ethylene glycol) phospholipid. The powder X-ray diffraction (XRD) patterns revealed that MnO is the main component of both MONs and WMONs and showed an increase of the Mn3O4 fraction in the WMONs. The analysis of the surface composition with X-ray photoelectron spectroscopy (XPS) indicated the presence of Mn and Mn (see the Supporting Information). On the basis of these observations, it was presumed that the as-synthesized MONs were passivated with Mn3O4 formed by their contact with air, even under an organic solvent, and that further oxidation occurred to form a thicker Mn3O4 shell when they were transferred into water. Very recently, the oxidation of the surface of MnO nanoparticles in air was also reported. The hollow interior of the HMONs was created by selective removal of the core MnO phase from the WMONs in acidic solution (Scheme 1). After being stirred at room

Fe3O4/MnO hybrid nanocrystals as a dual contrast agent for both T1- and T2-weighted liver MRI

To investigate whether it is possible to develop a dual magnetic resonance (MR) contrast agent, Fe(3)O(4)/MnO hybrid nanocrystals were modified to integrate the T(1) and T(2) contrast-enhancing abilities of each compound, and their characteristics as MR contrast agents were investigated. In vitro and in vivo investigations revealed that the Fe(3)O(4)/MnO dumbbell-shaped nanocrystal exerted a negative T(2) contrast effect in its intact form and also gave rise to a positive contrast effect in T(1)-weighted MR imaging by releasing Mn(2+) ions in a low pH environment. This induced organ-specific contrast enhancement for both T(1)- and T(2)-weighted in vivo MR imaging. The usefulness of the Fe(3)O(4)/MnO hybrid nanocrystals as dual contrast agents was evaluated by in vivo MR imaging of an orthotopic xenograft model of human hepatocellular carcinoma (HCC). After injection of the Fe(3)O(4)/MnO hybrid nanocrystals, dual contrast-enhanced MR images that synergistically combined the T(2) and T(1) contrast effects from the Fe(3)O(4) grain and released Mn(2+) ions were obtained by a single acquisition of MR imaging. This facilitated the detection of HCC with a high degree of conspicuity that could not be achieved with any single contrast agent.

Quantitative dynamic contrast-enhanced MRI for mouse models using automatic detection of the arterial input function

Dynamic contrast‐enhanced MRI (DCE‐MRI) is widely accepted for the evaluation of cancer. DCE‐MRI, a noninvasive measurement of microvessel permeability, blood volume and blood flow, is extremely useful for understanding disease mechanisms and monitoring therapeutic responses in preclinical research. For the accurate quantification of pharmacokinetic parameters using DCE‐MRI, determination of the arterial input function (AIF) from a large arterial vessel near the tumor is required. However, a manual determination of AIF in mouse MR images is often difficult because of the small spatial dimensions or the location of the tumor. In this study, we propose an algorithm for the automatic detection of AIF from mouse DCE‐MR images using Kendalls coefficient of concordance. The proposed method was tested with computer simulations and then applied to tumor‐bearing mice (nu2009=u20098). Results from computer simulations showed that the proposed algorithm is capable of categorizing simulated AIF signals according to their noise levels. We found that the resulting pharmacokinetic parameters computed from our method were comparable with those from the manual determination of AIF, with acceptable differences in Ktrans (5.14u2009±u20093.60%), ve (6.02u2009±u20093.22%), vp (5.10u2009±u20097.05%) and kep (5.38u2009±u20094.72%). The results of the current study suggest the usefulness of an automatically defined AIF using Kendalls coefficient of concordance for quantitative DCE‐MRI in mouse models for cancer evaluation. Copyright

Optimal Route for Mesenchymal Stem Cells Transplantation after Severe Intraventricular Hemorrhage in Newborn Rats

Recently, we showed that intracerebroventricular (IC) transplantation of human umbilical cord blood (UCB)-derived mesenchymal stem cells (MSCs) significantly attenuates posthemorrhagic hydrocephalus (PHH) and brain damage after severe IVH in newborn rats. This study was performed to determine the optimal route for transplanting MSCs for severe IVH by comparing IC transplantation, intravenous (IV) transplantation, and IV transplantation plus mannitol infusion. Severe IVH was induced by injecting 100 uL of blood into each ventricle of Sprague-Dawley rats on postnatal day 4 (P4). After confirming severe IVH with brain magnetic resonance imaging (MRI) at P5, human UCB-derived MSCs were transplanted at P6 by an IC route (1×105), an IV route (5×105), or an IV route with mannitol infused. Follow-up brain MRIs and rotarod tests were performed. At P32, brain tissue samples were obtained for biochemical and histological analyses. Although more MSCs localized to the brain after IC than after IV delivery, both methods were equally effective in preventing PHH; attenuating impaired rotarod test; increasing the number of TUNEL-positive cells, inflammatory cytokines, and astrogliosis; and reducing corpus callosal thickness and myelin basic protein expression after severe IVH regardless of mannitol co-infusion. Despite the superior delivery efficacy with IC than with the IV route, both IC and IV transplantation of MSCs had equal therapeutic efficacy in protecting against severe IVH. These findings suggest that the less invasive IV route might be a good alternative for clinically unstable, very preterm infants that cannot tolerate a more invasive IC delivery of MSCs.

Mn2+-doped silica nanoparticles for hepatocyte-targeted detection of liver cancer in T1-weighted MRI

With an aim to examine the possibility of developing a liver-specific MRI contrast agent that takes advantages of brightly enhanced MR images by Mn²⁺ whilst making up the limitations of the pre-developed contrast agent, the Mn²⁺-doped SiO₂ nanoparticles (Mn-SiO₂) were synthesized and their characteristics as MR contrast agents were investigated. The in vitro and in vivo investigations showed that Mn-SiO₂ has unique MR contrast-enhancing characteristics that activate positive contrast enhancement in T1-weighted MR images only under low pH conditions by liberating Mn²⁺ ions from MR inactive nanoparticles. The administration of Mn-SiO₂ to an orthotopic xenograft model of human hepatocellular carcinoma (HCC) resulted in a differentiation of enhancement periods between HCC and normal parenchyma tissues on T1-weighted MR images and consequently presented the duplicates of the highly contrast-enhanced liver image with an equal liver-to-HCC contrast ratio but opposite contrast. The Mn-SiO₂-enhanced MR imaging therefore allowed for the repetitive detection of the HCC within a single MR imaging session, which can help us to achieve more reliable diagnosis and characterization of liver lesions than is possible with any currently used Mn²⁺-based contrast agent. In addition, the in vivo biodistribution study also supported the effectiveness of Mn-SiO₂ nanoparticles as a liver-specific MRI contrast agent, which efficiently delivers and releases the T1-contrasting Mn²⁺ ions to targeted hepatocytes.

Altered white matter integrity and functional connectivity of hyperacute-stage cerebral ischemia in a rat model.

Ischemic stroke is accompanied by structural deformation and functional deficits in the affected hemisphere. Within a couple of hours after symptom onset, the accurate identification of brain characteristics is critical to design the therapeutic strategies and it can potentially improve overall brain tissue viability by minimizing irreversible brain damage. In this study, white matter integrity and functional connectivity within 2-4h after right middle cerebral artery occlusion in rats were investigated using multimodal magnetic resonance imaging. During this stage, diffusion tensor image (DTI) revealed that fractional anisotropy along the ipsilesional external capsule was slightly increased as compared with preoperative baseline. Resting state functional MRI (rs-fMRI) showed that the inter-hemispheric functional connectivities from primary motor (M1), primary somatosensory of forelimb (S1FL), and barrel field (S1BF) seeds were considerably reduced at the hyperacute stage. Fractional amplitudes of low frequency fluctuations (fALFF) from rs-fMRI were significantly enhanced at the hyperacute stage in the frequency spectrum between 0.01 and 0.08Hz. In addition, the changes in fALFF were negatively correlated with the number of functionally connected voxels in M1, S1FL and S1BF. Our results suggest that these techniques are useful tools to evaluate remarkable brain changes in the hyperacute stage of ischemic stroke.

Improvement of orthotopic lung cancer mouse model via thoracotomy and orotracheal intubation enabling in vivo imaging studies

Investigation of molecular mechanisms and the efficiency of novel therapeutics for the treatment and prevention of a disease require accurate and accessible preclinical models. Recent developments in personalized medicine employing molecular medicine concepts have favored mice because their genetic make-up is well known and easy to manipulate. For lung cancer, however, orthotopic models in mice are difficult to create due to their narrow glottis openings which act as obstacles to intubation. In the present study, we develop an orotracheal intubation device which gives a clearer view of the narrow mouse glottis and increases the success rate of intubation. We achieved anesthetization via orotracheal intubation using this novel device and then performed a thoracotomy by making an incision between the fourth and fifth intercostal ribs on the right side of the chest. Lung tumor cells were then inoculated at this site. Tumor formation was monitored through bioluminescence optical and magnetic resonance (MR) imagings, which was confirmed by histological analysis. Temperature drop (<35℃) and/or loss of body weight (>30% of the initial body weight) observed during any procedure were used as interruption criteria. This method exhibited high tumorigenicity (100%) and a low mortality rate (8%) at specific sites making it ideal for creating orthotopic lung tumor models and making it particularly useful for sequential follow-up studies using in vivo image analysis.