From MRI Contrast to Compatibility: Distinct Macrophage and Neutrophil Responses to Metal Oxide Nanoparticles versus Gadobutrol

Abstract Magnetic resonance imaging (MRI) relies on gadolinium-based contrast agents (GBCAs) that have recently been found to accumulate in blood cells and various organs in patients with normal renal function. These concerns have motivated development of alternative manganese- and iron-based platforms. While macrophages are commonly evaluated when designing novel contrast agents, very few studies test contrast agent interactions with neutrophils. Here, we systematically evaluated how contrast agent design and metal content affect off-target innate immune responses in RAW 264.7 macrophages and primary murine neutrophils. Manganese oxide (MnO) and iron oxide (Fe3O4) nanoparticles were compared against metal-free blank nanoparticles and the clinical GBCA gadobutrol (Gadavist). Contrast agents were assessed for their ability to influence T1/T2 MRI signal, cell uptake, ROS generation, and innate immune activation. Gadavist had the highest MRI signal enhancement in macrophages (%ΔR1= 75%) and neutrophils (%ΔR1= 175%), confirming leukocyte uptake. Flow cytometry revealed low cell-associated nanoparticle fractions but higher activation marker expression in macrophages and higher ROS levels in neutrophils. However, metal content did not significantly elevate activation markers or ROS compared to blank nanoparticles. While metal oxide nanoparticles induced minimal changes in neutrophil and macrophage cytokine release, Gadavist significantly enhanced multiple inflammatory cytokines that drive immune cell recruitment. Herein, metal oxide nanoparticles had a more favorable acute immune compatibility than Gadavist. Reduced off-target immune cell interactions should be desirable to maximize target-to-background specificity as contrast agents move toward in vivo assessment. These results support evaluating MRI contrast performance alongside innate immune compatibility to enhance contrast efficacy and safety.