Bioactive Molecules Delivery through Ferritin Nanoparticles: Sum Up of Current Loading Methods

Abstract

Ferritin (Ft) is a protein with a peculiar three-dimensional architecture. It is characterized by a hollow cage structure and is responsible for iron storage and detoxification in almost all living organisms. It has attracted the interest of the scientific community thanks to its appealing features, such as its nano size, thermal and pH stability, ease of functionalization, and low cost for large-scale production. Together with high storage capacity, these properties qualify Ft as a promising nanocarrier for the development of delivery systems for numerous types of biologically active molecules. In this paper, we introduce the basic structural and functional aspects of the protein, and summarize the methods employed to load bioactive molecules within the ferritin nanocage.

Keywords: bioactive molecules; drug delivery; encapsulation; ferritin nanocages; loading protocols.

Figure 1

(A) The 24-mer cage structure of classical ferritin (Ft) and of bacterioferritin (Bfr from Escherichia coli, PDB code: 1BFR [1]). (B) The 12-mer cage structure of Dps from Escherichia coli (PDB code: 1DPS [2]).

Figure 2

(A) Structure organization of the cage structure of ncapsulated ferritin from Rhodospirillum rubrum (EncFt; PDB code: 5DA5 [4]). (B) The single chain dimer is also reported.

Figure 3

Structure of the four-helix-bundle of the ferritin subunit. Each subunit and the connecting loops are indicated.

Figure 4

Organization of ferritin subunits to form (A) the four-fold channel C4 and (B) the three-fold channel C3 (PDB code: 5N27) [19].

Figure 5

Scheme of ferritin cargo-loading approaches.

Figure 6

Scheme of the in situ generation of Ft-CDDP.

Figure 7

Schematic drawings of the methods of preparation of Au/Pd bimetallic NPs in apoLFt. Au³⁺, Au⁰, Pd²⁺, and Pd⁰ atoms are colored red, orange, yellow, and brown, respectively. In scheme (a) the reduction occurs upon loading of both gold and palladium; in scheme (b) the two metals are reduced each one upon loading.

Figure 8

Subunit structure of Ru(p-cymene)-apoLFt. Ruthenium binding sites are shown as sticks and ruthenium atoms as dark red spheres [53].

Figure 9

Schematic illustration of the formation and working mechanism of ZnF₁₆Pc-loaded RFRT.

Figure 10

Model of ATHase within apoferritin. Enzyme cofactor is depicted as blue spheres.

Figure 11

Schematic illustration of siRNA loading within human H-chain ferritin.

Figure 12

Cartoon representation of the cage structures of (A) Auranofin-loaded horse spleen ferritin and (B) Auranofin-loaded human H-chain ferritin. Gold atoms are depicted as yellow spheres.

Figure 13

Schematic illustration of DOX loading within human H-chain ferritin by urea-based protocol.

Figure 14

Schematic representation of PREC design: two subunits of Pyrococcus furiosus ferritin (PfFtn) are linked by a peptide with an enterokinase cleavage site and a SUMO protein linked to the N-terminus of Sub-1.