Emulsomes meet S-layer proteins: an emerging targeted drug delivery system

Abstract

Here, the use of emulsomes as a drug delivery system is reviewed and compared with other similar lipidic nanoformulations. In particular, we look at surface modification of emulsomes using S-layer proteins, which are self-assembling proteins that cover the surface of many prokaryotic organisms. It has been shown that covering emulsomes with a crystalline S-layer lattice can protect cells from oxidative stress and membrane damage. In the future, the capability to recrystallize S-layer fusion proteins on lipidic nanoformulations may allow the presentation of binding functions or homing protein domains to achieve highly specific targeted delivery of drug-loaded emulsomes. Besides the discussion on several designs and advantages of composite emulsomes, the success of emulsomes for the delivery of drugs to fight against viral and fungal infections, dermal therapy, cancer, and autoimmunity is summarized. Further research might lead to smart, biocompatible emulsomes, which are able to protect and reduce the side effects caused by the drug, but at the same time are equipped with specific targeting molecules to find the desired site of action.

Fig. (1)

Schematic drawings of (A) a liposome and an emulsome; (B) S layer coated emulsome. The PLs surrounding liposomes and emulsomes, as well as the S-layer are not drawn up-to-scale.

Figure 2

TEM micrograph of replicas of freeze fractured emulsomes. The direction of Pt/C shadowing is indicated by an arrow in the upper right-hand corner. (A) Concave fracture face: Most part of the solid tripalmitin core was removed during the fracture process. Remnants of the multilayered PLs can be seen; (B) Convex fracture face exhibiting the cross-fractured multilayered PLs (double arrows). Each bar represents 100 nm (Adapted from [31]. Copyright ©2013 with permission from WILEY-VCH).

Figure 3

(A) TEM images of emulsomes coated with rSbpA-GG (i.e., S-layer proteins fused with double protein G domains); (B) Closer view to one rSbpA-GG coated emulsome. The rSbpA-GG layer assembles on the surface with square lattice symmetry as the wild type, and covers the emulsome entirely. The bar corresponds to 200 and 100 nm, respectively.