In vivo delivery, pharmacokinetics, biodistribution and toxicity of iron oxide nanoparticles

Abstract

Iron oxide nanoparticles (IONPs) have been extensively used during the last two decades, either as effective bio-imaging contrast agents or as carriers of biomolecules such as drugs, nucleic acids and peptides for controlled delivery to specific organs and tissues. Most of these novel applications require elaborate tuning of the physiochemical and surface properties of the IONPs. As new IONPs designs are envisioned, synergistic consideration of the body's innate biological barriers against the administered nanoparticles and the short and long-term side effects of the IONPs become even more essential. There are several important criteria (e.g. size and size-distribution, charge, coating molecules, and plasma protein adsorption) that can be effectively tuned to control the in vivo pharmacokinetics and biodistribution of the IONPs. This paper reviews these crucial parameters, in light of biological barriers in the body, and the latest IONPs design strategies used to overcome them. A careful review of the long-term biodistribution and side effects of the IONPs in relation to nanoparticle design is also given. While the discussions presented in this review are specific to IONPs, some of the information can be readily applied to other nanoparticle systems, such as gold, silver, silica, calcium phosphates and various polymers.

Fig. 1

Adsorption of the plasma proteins on the IONPs followed by their uptake by Kupffer cells and their accumulation in liver; Presence of PEG prevents the opsonization and decreases the uptake of the IONPs by macrophages. Re-printed with permission from ref. . Copyright 2011, Future Medicine.

Fig. 2

(a) Scanning electron microscopy (SEM) image of the liver sinusoids. (b) Kupffer cells located in liver sinusoids phagocytize the IONPs from the bloodstream. Adapted with permission from refs. and . Copyrights 2002, Elsevier B. V. and 2011, American Chemical Society.

Fig. 3

The spleen microstructural anatomy and pathway of the IONPs entering the spleen through its central arteriole. This artery terminates in highly porous small capillaries that direct the IONP into the marginal zones around the white pulp where macrophages actively take up the nanoparticles. Re-printed with permission from ref. . Copyright 2009, Nature Publishing Group.

Fig. 4

Pathway of the IONPs in lymph node system. IONPs get taken up from the blood vessel by the lymph node macrophages (histiocytes) and then get shuttled to the lymph vessel through afferent lymphatics. Adapted with permission from ref. . Copyright 2003, Massachusetts Medical Society.

Fig. 5

(A) Excretion pathway of the IONPs or their degradation products through kidney. IONPs enter the glomerular capillaries through the afferent arterioles. IONPs smaller than 10-15nm, their detached coating molecules, therapeutic agents (e.g. siRNA) or degradation bi-products present in the blood can pass the glomerular endothelium and fenestrations between the podocytes, where they actually get transferred to renal tubules and are excreted in the urine via the bladder. Transmission electron microscopy (TEM) images in parts (B), (C) and (D) show that nanoparticles (NP) were trapped in these fenestrae due to their large sizes (~60-100nm). (BM: Basement membrane; FB: Filtration barrier, (I/D)-NP: (intact/disassembling) nanoparticle; P: podoyctes; U: Urinary space; PF: podocyte foot process; M: Mesangium, PC: peritubule capillary; E: Endothelial cell; R: Erythrocyte). Re-printed with permission from ref. . Copyright 2012, National Academy of Sciences.

Fig. 6

Schematic showing the size dependent physiological barriers against nanoparticles blood circulation. (A) In human kidneys, nanoparticles with d_H < 15 nm in diameter are filtered out, thus imposing a lower size limit for designing long circulating nanoparticles. (B) Sinusoidal capillaries in the liver are fenestrated (50-180 nm) and lined with the Kupffer cells, which rapidly uptake large nanoparticles or agglomerates tagged with opsonins, and smaller nanoparticles are trapped in the Disse space and can be taken up by hepatocytes. Meanwhile, nanoparticles <100 nm in diameter with non-fouling (prevent protein adsorption) and non-immunogenic (prevent immune response) coatings continue circulating. (C) The Spleen imposes the true upper limit in optimal size for circulation – nanoparticles larger than about 200 nm get trapped in the marginal zones and red pulp, where they are sequestered by the splenic macrophages. (D) Finally, opsonization is the tagging of nanoparticles with specialized proteins called opsonins for removal by phagocytic cells of mononuclear phagocytic system (MPS), which includes the Kupffer cells in the liver and the splenic macrophages in the marginal zones and red pulp.

Fig. 7

Single crystalline iron oxide nanocubes (left) and their biodegradation in crystallographic directions with higher atomic surface energies after incubation in lysosome-like solution (right). Adapted with permission from ref. . Copyright 2013, American Chemical Society.

Fig. 8

(A) Mushroom-like configuration of the coating molecules on the surface of the IONPs which results in a lower density of the coating molecules and (B) brush-type assembly of the coating molecules which provides a high density coating layer. Re-printed with permission from ref. . Copyright 2011, Future Medicine.

Fig. 9

(A) The half-lives of the dextran coated IONPs in different types of knockout mice (each lacking a specific plasma protein). The half-lives in various genetically engineered knockout mice (MBL, IgG, HPRG, HMWK, Fibronectin, Vitronectin, Fibrinogen and complement C3 deficient mice) were almost similar to their half-life in wild type (WT) control mice with all plasma proteins present in blood. Mice treated with Clodronate liposomes had impaired liver phagocytic function which served as a control (right bar). (MBL: mannose-binding lectins; Immunoglobulin G: IgG; HPRG: histidine–proline rich glycoprotein; HMWK: high molecular weight kininogen (HMWK)). (B) Histology of the liver sections confirm the results in part (A) and show that the Kupffer cells recognize and take up these IONPs (green dots due to presence of fluorescent molecules on their surface) regardless of the type of the proteins adsorbed to the surface of the nanoparticles after their injection. (Panel labels: 1, HMWK-deficient; 2, wild type; 3, complement C3-deficient; 4, MBL-deficient; 5, clodronate-treated mice). Re-printed with permission from ref. . Copyright 2009, Elsevier B. V.

Fig. 10

Comparison of the typical blood capillaries found in most parts of the body (left) with the blood brain barrier (BBB, right). Small hydrophilic molecules can diffuse between blood and interstitial fluids through the pores between the endothelial cells in normal capillaries. Hydrophobic molecules and large size proteins can only pass this barrier by transcytosis. Endothelial cells in brain capillaries are connected by tight junctions. Proteins transcytosis is not possible in BBB and only selected hydrophilic molecules can pass the barrier by mediated carriers. Hydrophobic molecules can cross the BBB by transcytosis. Re-printed with permission from ref. . Copyright 2008, Pearson Education, Inc.

Fig. 11

(A) Tumors leaky vasculators and their enhanced permeability and retention (EPR). (B) Presence of an externally applied magnetic field can increase the accumulation of the IONPs in tumor area. Re-printed with permission from ref. . Copyright 2012, Elsevier B. V.

Fig. 12

Ferritin (~13nm) is the main form of iron storage in the liver after degradation of IONPs in macrophages. It is formed from a protein shell (~13nm) surrounding iron oxide ultrasmall nanoparticles in their central cavity (~8nm). Re-printed with permission from ref. . Copyright 2010, Elsevier B. V.

Fig. 13

IONPs biodegradation and general iron transport and metabolism pathway in the body. The intravenously injected IONPs, with hydrodynamic sizes larger than 10-15nm, get degraded in MPS (or RES) macrophages and free iron ions transform to ferritin and hemosiderin iron-protein complexes. Ferritin can transform to transferrin and then get transported to bone marrow, where they are used for making hemoglobin in red blood cells (RBC) that circulate in the body. A part of this iron also forms myoglobin, an iron-protein complex carrying oxygen to muscles. Senescent RBCs are fragile and burst in the tight capillary spaces of the red pulp in the spleen and release their hemoglobin. This can cause an increase in the amount of iron in the spleen. MPS macrophages then phagocytize these hemoglobin molecules, form ferritin and again transform them into transferrin, which can go back to bone marrow to make new RBCs or get stored in the liver hepatocytes in the form of ferritin.