Reactive oxygen species-related activities of nano-iron metal and nano-iron oxides

Abstract

Nano-iron metal and nano-iron oxides are among the most widely used engineered and naturally occurring nanostructures, and the increasing incidence of biological exposure to these nanostructures has raised concerns about their biotoxicity. Reactive oxygen species (ROS)-induced oxidative stress is one of the most accepted toxic mechanisms and, in the past decades, considerable efforts have been made to investigate the ROS-related activities of iron nanostructures. In this review, we summarize activities of nano-iron metal and nano-iron oxides in ROS-related redox processes, addressing in detail the known homogeneous and heterogeneous redox mechanisms involved in these processes, intrinsic ROS-related properties of iron nanostructures (chemical composition, particle size, and crystalline phase), and ROS-related bio-microenvironmental factors, including physiological pH and buffers, biogenic reducing agents, and other organic substances.

Keywords: Iron oxide; Metallic iron; Nanoparticle; Reactive oxygen species; Toxicity.

Fig. 1

Schematic illustration of peroxidase-like activity-induced cytotoxicity by iron oxide nanoparticles (IONPs). IONPs are trapped in acidic lysosomes when internalized into cells, so they catalyze decomposition of H₂O₂ to produce hydroxyl radicals through peroxidase-like activity; however, in neutral cytosol, IONPs would decompose H₂O₂ through catalase-like activity. Note. From “Dual enzyme-like activities of iron oxide nanoparticles and their implication for diminishing cytotoxicity,” by Z. Chen, J.J. Yin, Y.T. Zhou, et al, 2012, ACS Nano, 6, p. 4001–12. Copyright 2012, ACS Publications. Reprinted with permission.

Fig. 2

Scheme for ^•OH free radical generation by iron oxide nanoparticles (NPs) in bio-microenvironments. (A) ^•OH generation at the nanobio interface of Fe₂O₃ NPs; (B) chemical processes of ^•OH generation by Fe₂O₃ NPs; (C) intracellular ^•OH free radical generation: dissolution or in situ reductive dissolution of magnetic iron oxide NPs may occur in the acidic lysosomal microenvironment, which depends on surface hydroxylation and surface Fe oxidation state of iron oxide NPs; the free Fe ions or NPs can react with hydrogen peroxide and superoxide in mitochondria and cytoplasm to produce highly reactive ^•OH via homogeneous or heterogeneous Fe(II)/Fe(III) catalytic Fenton/Haber-Weiss type reaction. Note. From “Physicochemical origin for free radical generation of iron oxide nanoparticles in biomicroenvironment: catalytic activities mediated by surface chemical states,” by B. Wang, J.J. Yin, X.Y. Zhou, et al, 2013, J Phys Chem C, 117, p. 383–92. Copyright 2012, ACS Publications. Reprinted with permission.