Repeated Injection of Very Small Superparamagnetic Iron Oxide Particles (VSOPs) in Murine Atherosclerosis: A Safety Study.

Citrate-coated electrostatically stabilized very small superparamagnetic iron oxide particles (VSOPs) have been successfully tested as magnetic resonance angiography (MRA) contrast agents and are promising tools for molecular imaging of atherosclerosis. Their repeated use in the background of pre-existing hyperlipidemia and atherosclerosis has not yet been studied. This study aimed to investigate the effect of multiple intravenous injections of VSOPs in atherosclerotic mice. Taurine-formulated VSOPs (VSOP-T) were repeatedly intravenously injected at 100 µmol Fe/kg in apolipoprotein E-deficient (ApoE KO) mice with diet-induced atherosclerosis. Angiographic imaging was carried out by in vivo MRI. Magnetic particle spectrometry was used to detect tissue VSOP content, and tissue iron content was quantified photometrically. Pathological changes in organs, atherosclerotic plaque development, and expression of hepatic iron-related proteins were evaluated. VSOP-T enabled the angiographic imaging of heart and blood vessels with a blood half-life of one hour. Repeated intravenous injection led to VSOP deposition and iron accumulation in the liver and spleen without affecting liver and spleen pathology, expression of hepatic iron metabolism proteins, serum lipids, or atherosclerotic lesion formation. Repeated injections of VSOP-T doses sufficient for MRA analyses had no significant effects on plaque burden, steatohepatitis, and iron homeostasis in atherosclerotic mice. These findings underscore the safety of VSOP-T and support its further development as a contrast agent and molecular imaging tool.