Size-Dependent Oxygen Vacancy of Iron Oxide Nanoparticles.

Prior research has highlighted the reduction of iron oxide nanoparticle (IONPs) sizes to the "ultra-small" dimension as a pivotal approach in developing T1-MRI contrast agents, and the enhancement in T1 contrast performance with the reducing size is usually attributed to the increased specific surface area and weakened magnetization. Nonetheless, as the size decreases, the variation in surface defects, particularly oxygen vacancy (VO) defects, significantly impacts the T1 imaging efficacy. In this study, the VO on IONPs is meticulously investigated through XPS, Raman, and EPR spectroscopy. As the nanoparticle size decreased, the VO concentration rose initially but subsequently declined, with the peak concentration observed in the size of 8.27 nm. Further insights gained from synchrotron XAS analysis and DFT calculations indicate that both surface tension and phase transition in IONPs contribute to alterations in the Fe─O bond length, thereby influencing the VO formation energy across varying nanoparticle sizes. The MRI tests reveal that the VO in IONPs serve as pivotal sites for the attachment of water molecules to iron ions, and IONPs with fewer VO exhibited a deterioration in T1-MRI contrast effects. This research may provide a deeper understanding of the relationship between T1 contrast performance and the size of IONPs.

Unveiling the next generation of MRI contrast agents: current insights and perspectives on ferumoxytol-enhanced MRI.

Contrast-enhanced magnetic resonance imaging (CE-MRI) is a pivotal tool for global disease diagnosis and management. Since its clinical availability in 2009, the off-label use of ferumoxytol for ferumoxytol-enhanced MRI (FE-MRI) has significantly reshaped CE-MRI practices. Unlike MRI that is enhanced by gadolinium-based contrast agents, FE-MRI offers advantages such as reduced contrast agent dosage, extended imaging windows, no nephrotoxicity, higher MRI time efficiency and the capability for molecular imaging. As a leading superparamagnetic iron oxide contrast agent, ferumoxytol is heralded as the next generation of contrast agents. This review delineates the pivotal clinical applications and inherent technical superiority of FE-MRI, providing an avant-garde medical-engineering interdisciplinary lens, thus bridging the gap between clinical demands and engineering innovations. Concurrently, we spotlight the emerging imaging themes and new technical breakthroughs. Lastly, we share our own insights on the potential trajectory of FE-MRI, shedding light on its future within the medical imaging realm.

Correction to: Unveiling the next generation of MRI contrast agents: current insights and perspectives on ferumoxytol-enhanced MRI.

[This corrects the article DOI: 10.1093/nsr/nwae057.].

Magnetic Delivery of Antigen-Loaded Magnetic Liposomes for Active Lymph Node Targeting and Enhanced Anti-Tumor Immunity.

Therapeutic cancer vaccines offer the greatest advantage of enhancing antigen-specific immunity against tumors, particularly for immunogenic tumors, such as melanoma. However, clinical responses remain unsatisfactory, primarily due to inadequate T cell priming and the development of acquired immune tolerance. A major obstacle lies in the inefficient uptake of antigen by peripheral dendritic cells (DCs) and their migration to lymph nodes for antigen presentation. In this context, the magnetic delivery of antigen-loaded magnetic liposomes (Ag-MLs) to actively target lymph node, is proposed. These magnetic responsive liposomes contain soluble mouse melanoma lysate and iron oxide nanoparticles in the core, along with the immunostimulatory adjuvant CpG-1826 incorporated into the lipid bilayer. When applied through magnetic targeting in the mouse melanoma model, Ag-MLs accumulate significantly in the target lymph nodes. This accumulation results in increased population of active DCs in lymph nodes and cytotoxic T lymphocytes (CTLs) within tumors, correlating with effective tumor growth inhibition. Overall, this study demonstrates the potential of magnetic targeting as an effective strategy for delivering cancer vaccines and activating the immune response, offering a novel platform for cancer immunotherapies.

Extracellular magnetic labeling of biomimetic hydrogel-induced human mesenchymal stem cell spheroids with ferumoxytol for MRI tracking.

Labeling of mesenchymal stem cells (MSCs) with superparamagnetic iron oxide nanoparticles (SPIONs) has emerged as a potential method for magnetic resonance imaging (MRI) tracking of transplanted cells in tissue repair studies and clinical trials. Labeling of MSCs using clinically approved SPIONs (ferumoxytol) requires the use of transfection reagents or magnetic field, which largely limits their clinical application. To overcome this obstacle, we established a novel and highly effective method for magnetic labeling of MSC spheroids using ferumoxytol. Unlike conventional methods, ferumoxytol labeling was done in the formation of a mechanically tunable biomimetic hydrogel-induced MSC spheroids. Moreover, the labeled MSC spheroids exhibited strong MRI T2 signals and good biosafety. Strikingly, the encapsulated ferumoxytol was localized in the extracellular matrix (ECM) of the spheroids instead of the cytoplasm, minimizing the cytotoxicity of ferumoxytol and maintaining the viability and stemness properties of biomimetic hydrogel-induced MSC spheroids. This demonstrates the potential of this method for post-transplantation MRI tracking in the clinic.

Diagnostic Performance and Safety of a Novel Ferumoxytol-Enhanced Coronary Magnetic Resonance Angiography.

BACKGROUND: Currently, noninvasive arteriography for the diagnosis of coronary artery disease is clinically limited to the computed tomography scanning, where patients have to be exposed to the radiation and risks associated with iodinated contrast. We aimed to investigate the diagnostic performance and safety of a novel ferumoxytol-enhanced coronary magnetic resonance angiography (CMRA) in patients with suspected coronary artery disease. METHODS: Thirty patients, 19 males, with a median age of 63 years old, and 17 with renal insufficiency, who were scheduled for invasive coronary angiography, were enrolled. Ferumoxytol was administered intravenously with a dose of 3 mg/kg during CMRA. Images were acquired with an ECG-triggered, navigator-gated, inversion recovery-prepared 3D fast low-angle shot sequence, and the image quality was assessed by a 4-point scale. Eighteen-segment coronary artery model was adopted to evaluate the visibility of the coronary arteries, and the image quality and stenosis were evaluated in nine segments. The diagnostic performance of CMRA is described as sensitivity, specificity, positive and negative predictive values, and accuracy with the invasive coronary angiography results as reference. The patients' vital signs were monitored during CMRA, and their hepatic and renal functions were followed up for 3 months to evaluate the safety of ferumoxytol. RESULTS: Two hundred fifty-two of the 270 study segments were identified by CMRA, and their quality score reached 3.6±0.7. Referring to the invasive coronary angiography results, the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of ferumoxytol-enhanced CMRA reached 100.0%, 66.7%, 92.3%, 100.0%, and 93.3% respectively in patient-based analysis; 91.4%, 90.9%, 86.5%, 94.3%, and 91.1%, respectively in vessel-based analysis; and 92.3%, 96.7%, 83.7%, 98.6%, and 96.0%, respectively in segment-based analysis. No ferumoxytol-related adverse event was observed during the 3-month follow-up. CONCLUSIONS: Ferumoxytol-enhanced CMRA demonstrated good diagnostic performance and excellent safety in the diagnosis of significant coronary stenosis, providing an alternative to coronary computed tomography angiography for the diagnosis of coronary artery disease. REGISTRATION: URL: https://www. CLINICALTRIALS: gov; Unique identifier: NCT05032937.