Humics-Functionalized Iron(III) Oxyhydroxides as Promising Nanoferrotherapeutics: Synthesis, Characterization, and Efficacy in Iron Delivery

Iron deficiency anemia (IDA) remains a global health challenge. This study pioneers the use of humic substances (HS) as natural, biocompatible macroligands to develop safer and more effective nanoferrotherapeutics. We synthesized a series of nanoscale Fe(III) oxyhydroxide complexes stabilized by different HS, employing various solvents (ethanol, isopropanol, and acetone) and precipitation methods to isolate fractions with optimized properties. The nanocomposites were comprehensively characterized using inductively coupled plasma atomic emission spectrometry, total organic carbon analysis, X-ray diffraction, transmission electron microscopy, and Mössbauer spectroscopy. Cytotoxicity and iron bioavailability of all HS-Fe(III) formulations were assessed in Caco-2 intestinal epithelial cells. The type of HS and precipitation conditions significantly influenced the nanocomposites’ properties, yielding spherical nanoparticles (1–2 nm) of ferrihydrite or goethite. Physicochemical analysis confirmed that solvent-driven fractionation effectively tailored the nanocomposites’ size, crystallinity, and elemental composition. All HS-Fe(III) formulations demonstrated exceptional cytocompatibility, starkly contrasting the significant cytotoxicity of the reference drug Ferrum Lek®. Several complexes, particularly CHSFe-Et67, surpassed Ferrum Lek® in cellular iron uptake efficiency. We conclude that HS are a highly promising platform for developing effective and safe iron-delivery nanoferrotherapeutics, leveraging their natural polyfunctionality to enhance bioavailability and mitigate toxicity.