The fate of iron nanoparticles used for treatment of iron deficiency in blood using mass-spectrometry based strategies

The release of iron from iron nanoparticles (NPs) used as parenteral formulations appears to be influenced by the size and surface properties of the colloidal iron complex and the matrix. A clinically applied product Venofer® has been used as a model formulation to establish adequate analytical strategies to evaluate the fate of iron nanoparticles (NPs) in blood. First, the preparation was characterized by high resolution transmission electron microscopy (HR-TEM), dynamic light scattering (DLS) and UV-vis absorption spectroscopy. This revealed the presence of monodisperse iron NPs with a hydrodynamic diameter of ∼15 nm and an iron core of ∼4 nm. Venofer® was then incubated with serum and whole blood in a quantitative study on the iron bioavailability from these NPs. Iron was speciated and quantified by using inductively coupled plasma mass spectrometry (ICP-MS). Iron solubilization levels of up to 42% were found in both fluids using isotope dilution of iron for quantification within the first hour of incubation even in the absence of the reticulo-endothelial system. The monitoring of the iron-containing proteins present in serum was conducted by high-performance liquid chromatography with ICP-MS detection. It indicated that the dissolved iron ions are bound to transferrin. Quantitative speciation studies using isotope pattern deconvolution experiments concluded that the released iron saturated almost completely (up to 90%) the metal binding sites of transferrin. The remaining iron appeared also associated to albumin and, to a lesser extent, forming smaller sized particles. Thus, the methods presented here provide new insights into the fate of Venofer® nanoparticles and may be applied to other formulations.