Superparamagnetic iron oxide based nanoprobes for imaging and theranostics

Superparamagnetic iron oxide nanoparticles for in vivo molecular and cellular imaging

In the last decade, the biomedical applications of nanoparticles (NPs) (e.g. cell tracking, biosensing, magnetic resonance imaging (MRI), targeted drug delivery, and tissue engineering) have been increasingly developed. Among the various NP types, superparamagnetic iron oxide NPs (SPIONs) have attracted considerable attention for early detection of diseases due to their specific physicochemical properties and their molecular imaging capabilities. A comprehensive review is presented on the recent advances in the development of in vitro and in vivo SPION applications for molecular imaging, along with opportunities and challenges.

Nanoparticles in magnetic resonance imaging: from simple to dual contrast agents

Magnetic resonance imaging (MRI) has become one of the most widely used and powerful tools for noninvasive clinical diagnosis owing to its high degree of soft tissue contrast, spatial resolution, and depth of penetration. MRI signal intensity is related to the relaxation times (T₁, spin–lattice relaxation and T₂, spin–spin relaxation) of in vivo water protons. To increase contrast, various inorganic nanoparticles and complexes (the so-called contrast agents) are administered prior to the scanning. Shortening T₁ and T₂ increases the corresponding relaxation rates, 1/T₁ and 1/T₂, producing hyperintense and hypointense signals respectively in shorter times. Moreover, the signal-to-noise ratio can be improved with the acquisition of a large number of measurements. The contrast agents used are generally based on either iron oxide nanoparticles or ferrites, providing negative contrast in T₂-weighted images; or complexes of lanthanide metals (mostly containing gadolinium ions), providing positive contrast in T₁-weighted images. Recently, lanthanide complexes have been immobilized in nanostructured materials in order to develop a new class of contrast agents with functions including blood-pool and organ (or tumor) targeting. Meanwhile, to overcome the limitations of individual imaging modalities, multimodal imaging techniques have been developed. An important challenge is to design all-in-one contrast agents that can be detected by multimodal techniques. Magnetoliposomes are efficient multimodal contrast agents. They can simultaneously bear both kinds of contrast and can, furthermore, incorporate targeting ligands and chains of polyethylene glycol to enhance the accumulation of nanoparticles at the site of interest and the bioavailability, respectively. Here, we review the most important characteristics of the nanoparticles or complexes used as MRI contrast agents.

Manganese doped iron oxide theranostic nanoparticles for combined T1 magnetic resonance imaging and photothermal therapy

Photothermal therapy (PTT) is a noninvasive and convenient way to ablate tumor tissues. Integrating PTT with imaging technique could precisely identify the location and the size of tumor regions, thereby significantly improving the therapeutic efficacy. Magnetic resonance imaging (MRI) is widely used in clinical diagnosis due to its superb spatial resolution and real-time monitoring feature. In our work, we developed a theranostic nanoplatform based on manganese doped iron oxide (MnIO) nanoparticles modified with denatured bovine serum albumin (MnIO-dBSA). The in vitro experiment revealed that the MnIO nanoparticles exhibited T1-weighted MRI capability (r1 = 8.24 mM(-1) s(-1), r2/r1 = 2.18) and good photothermal effect under near-infrared laser irradiation (808 nm). Using 4T1 tumor-bearing mice as an animal model, we further demonstrated that the MnIO-dBSA composites could significantly increase T1 MRI signal intensity at the tumor site (about two times) and effectively ablate tumor tissues with photoirradiation. Taken together, this work demonstrates the great potential of the MnIO nanoparticles as an ideal theranostic platform for efficient tumor MR imaging and photothermal therapy.

In vivo multimodal magnetic particle imaging (MPI) with tailored magneto/optical contrast agents

Magnetic Particle Imaging (MPI) is a novel non-invasive biomedical imaging modality that uses safe magnetite nanoparticles as tracers. Controlled synthesis of iron oxide nanoparticles (NPs) with tuned size-dependent magnetic relaxation properties is critical for the development of MPI. Additional functionalization of these NPs for other imaging modalities (e.g. MRI and fluorescent imaging) would accelerate screening of the MPI tracers based on their in vitro and in vivo performance in pre-clinical trials. Here, we conjugated two different types of poly-ethylene-glycols (NH2-PEG-NH2 and NH2-PEG-FMOC) to monodisperse carboxylated 19.7 nm NPs by amide bonding. Further, we labeled these NPs with Cy5.5 near infra-red fluorescent (NIRF) molecules. Bi-functional PEG (NH2-PEG-NH2) resulted in larger hydrodynamic size (∼98 nm vs. ∼43 nm) of the tracers, due to inter-particle crosslinking. Formation of such clusters impacted the multimodal imaging performance and pharmacokinetics of these tracers. We found that MPI signal intensity of the tracers in blood depends on their plasmatic clearance pharmacokinetics. Whole body mice MPI/MRI/NIRF, used to study the biodistribution of the injected NPs, showed primary distribution in liver and spleen. Biodistribution of tracers and their clearance pathway was further confirmed by MPI and NIRF signals from the excised organs where the Cy5.5 labeling enabled detailed anatomical mapping of the tracers.in tissue sections. These multimodal MPI tracers, combining the strengths of each imaging modality (e.g. resolution, tracer sensitivity and clinical use feasibility) pave the way for various in vitro and in vivo MPI applications.

Potential applications of magnetic particles to detect and treat Alzheimer's disease

Nanotechnology is an exciting and promising scientific discipline. At the nanoscale, a material displays novel physical properties that offer many new and beneficial products and applications. In particular, magnetic nanoparticles - a core/shell nanoparticle - present considerable diagnostic and therapeutic potentials, and superparamagnetic iron oxide nanoparticles (SPIONs) are considered promising theranostic tools. Alzheimer's disease (AD) is a neurodegenerative disorder that predominantly affects people over 65 years of age. The disease is characterized by the presence of extracellular plaques in the brain which are formed by interwoven fibrils composed of variants of the β-amyloid peptide. Medication can temporarily retard worsening of symptoms, but only in the first stages of the disease; early detection is thus of crucial importance. This minireview covers the progress made in research on the use of magnetic nanoparticles for ex vivo and/or in vivo detection and diagnosis of AD by means of magnetic resonance imaging (MRI), or to label peptides and fibrils. Of particular importance is the use of these nanoparticles to detect AD biomarkers in biological fluids. A description is given of the bio-barcode amplification assay using functionalized magnetic particles, as well as the use of such nanoparticles as a system for inhibiting or delaying the assembly of peptide monomers into oligomers and fibrils. Lastly, a brief overview is given of possible future lines of research in this.

Glycosaminoglycan-targeted iron oxide nanoparticles for magnetic resonance imaging of liver carcinoma

To develop an efficient probe for targeted magnetic resonance (MR) imaging of liver carcinoma, the surface modification of superparamagnetic iron oxide nanoparticles (SPIONs) was carried out by conjugating a naturally-occurring glycosaminoglycan with specific biological recognition to human hepatocellular liver carcinoma (HepG2) cells. These modified SPIOs have good water dispersibility, superparamagnetic property, cytocompatibility and high magnetic relaxivity for MR imaging. When incubated with HepG2 cells, they demonstrated significant cellular uptake and specific accumulation, as confirmed by Prussian blue staining and confocal microscopy. The in vitro MR imaging of HepG2 cells and in vivo MR imaging of HepG2 tumors confirmed their effectiveness for targeted MR imaging of liver carcinoma.

Toxicity evaluation of Gd2O3@SiO2 nanoparticles prepared by laser ablation in liquid as MRI contrast agents in vivo

Poor toxicity characterization is one obstacle to the clinical deployment of Gd₂O₃@ SiO₂ core-shell nanoparticles (Gd-NPs) for use as magnetic resonance (MR) imaging contrast agents. To date, there is no systematic toxicity data available for Gd-NPs prepared by laser ablation in liquid. In this article, we systematically studied the Gd-NPs’ cytotoxicity, apoptosis in vitro, immunotoxicity, blood circulation half-life, biodistribution and excretion in vivo, as well as pharmacodynamics. The results show the toxicity, and in vivo MR data show that these NPs are a good contrast agent for preclinical applications. No significant differences were found in cell viability, apoptosis, and immunotoxicity between our Gd-NPs and Gd in a DTPA (diethylenetriaminepentaacetic acid) chelator. Biodistribution data reveal a greater accumulation of the Gd-NPs in the liver, spleen, lung, and tumor than in the kidney, heart, and brain. Approximately 50% of the Gd is excreted via the hepatobiliary system within 4 weeks. Furthermore, dynamic contrast-enhanced T1-weighted MR images of xenografted murine tumors were obtained after intravenous administration of the Gd-NPs. Collectively, the single step preparation of Gd-NPs by laser ablation in liquid produces particles with satisfactory cytotoxicity, minimal immunotoxicity, and efficient MR contrast. This may lead to their utility as molecular imaging contrast agents in MR imaging for cancer diagnosis.

Uptake and metabolism of iron oxide nanoparticles in brain cells

Magnetic iron oxide nanoparticles (IONPs) are used for various applications in biomedicine, for example as contrast agents in magnetic resonance imaging, for cell tracking and for anti-tumor treatment. However, IONPs are also known for their toxic effects on cells and tissues which are at least in part caused by iron-mediated radical formation and oxidative stress. The potential toxicity of IONPs is especially important concerning the use of IONPs for neurobiological applications as alterations in brain iron homeostasis are strongly connected with human neurodegenerative diseases. Since IONPs are able to enter the brain, potential adverse consequences of an exposure of brain cells to IONPs have to be considered. This article describes the pathways that allow IONPs to enter the brain and summarizes the current knowledge on the uptake, the metabolism and the toxicity of IONPs for the different types of brain cells in vitro and in vivo.

Techniques for physicochemical characterization of nanomaterials

Advances in nanotechnology have opened up a new era of diagnosis, prevention and treatment of diseases and traumatic injuries. Nanomaterials, including those with potential for clinical applications, possess novel physicochemical properties that have an impact on their physiological interactions, from the molecular level to the systemic level. There is a lack of standardized methodologies or regulatory protocols for detection or characterization of nanomaterials. This review summarizes the techniques that are commonly used to study the size, shape, surface properties, composition, purity and stability of nanomaterials, along with their advantages and disadvantages. At present there are no FDA guidelines that have been developed specifically for nanomaterial based formulations for diagnostic or therapeutic use. There is an urgent need for standardized protocols and procedures for the characterization of nanoparticles, especially those that are intended for use as theranostics.

Ce3/4+ cation-functionalized maghemite nanoparticles towards siRNA-mediated gene silencing

b-PEI₂₅-decorated [CeL_n]^3/4+-doped maghemite (γ-Fe₂O₃) nanoparticles were prepared for siRNA-mediated gene silencing using coordination chemistry as an inorganic way of functionalization.