Liposomes as Tools to Improve Therapeutic Enzyme Performance

Abstract

The drugs concept has changed during the last few decades, meaning the acceptance of not only low molecular weight entities but also macromolecules as bioagent constituents of pharmaceutics. This has opened a new era for a different class of molecules, namely proteins in general and enzymes in particular. The use of enzymes as therapeutics has posed new challenges in terms of delivery and the need for appropriate carrier systems. In this review, we will focus on enzymes with therapeutic properties and their applications, listing some that reached the pharmaceutical market. Problems associated with their clinical use and nanotechnological strategies to solve some of their drawbacks (i.e., immunogenic reactions and low circulation time) will be addressed. Drug delivery systems will be discussed, with special attention being paid to liposomes, the most well-studied and suitable nanosystem for enzyme delivery in vivo. Examples of liposomal enzymatic formulations under development will be described and successful pre-clinical results of two enzymes, L-Asparaginase and Superoxide dismutase, following their association with liposomes will be extensively discussed.

Keywords: drug delivery systems; liposomes; therapeutic enzymes.

Figure 1

Schematic representation of different types of liposomes: (A)—Conventional liposome loaded with hydrophilic enzyme in the internal aqueous space, and hydrophobic, amphipathic and acylated (hydrophilic enzyme linked to fatty acid chains) enzymes in the lipid bilayer; (B)—Enzyme-loaded liposomes containing lipids linked to polyethylene glycol (PEG), called long-circulating liposomes; (C)—Enzyme-loaded liposomes containing simultaneously PEG and enzymes at liposome surface or linked to functionalized PEG; (D)—Enzyme-loaded ultra-deformable liposomes, Transfersomes), with the non-uniformly distributed edge-active components at the stressed sites for membrane deformation. Vesicle D was intentionally drawn in an oval shape to represent the deformity that characterizes it and that is caused by the edge activator molecules. Adapted from Torchilin et al. 2005 [35].