Over the last decade, antimicrobial peptides (AMPs) have emerged as a promising alternative for treatment of various infections. A large variety of AMPs have been identified and isolated from plants, animals and humans. The benefits of using AMPs are that they act by disrupting the bacteria membranes, a mechanism that is fast and non-specific. Therefore bacteria are not prone to develop high level resistance towards these compounds in the same extent as towards conventional antibiotics. AMPs are in general rather small (10-40 amino acid residues), cationic and amphiphilic compounds with a diversity in secondary structure which can be altered to different extent upon membrane interaction. Their structure has been developed for millenia during evolution and is today well preserved.
AMPs have been assessed, analyzed and modified in order to increase their function and efficiency for future drug delivery applications. In humans, AMPs are naturally present in high concentrations in tissues frequently exposed to pathogens, such as the skin, lungs, and gastrointestinal tract. AMPs have a variety of functions besides having a broad-spectrum antibacterial effect. They can be antifungal, antiviral and have a significant immunoregulatory role including anti-inflammatory properties, which is a significant advantage in wound healing. The two major families of mammalian antimicrobial peptides, defensins and cathelicidins, act immunomodulatory by stimulating chemotaxis and chemokine production, wound healing, angiogenesis and dendritic cell activation, in addition to their direct antimicrobial activity. AMPs also have shown potential in prevention and breakdown of biofilms.
Although large efforts in research and development have been directed towards the area of AMPs, only a few candidates have reached later stages of clinical trials and to date no product based on AMPs has reached the market. One of the main reasons is the challenges related to stability of peptides in the formulations and after administration, which leads to reduced efficiency. Proteolytic degradation and self-aggregation are typical problems observed with these compounds. In order to increase efficiency and stability, various approaches to modify the peptide structure have been employed. However, these challenges can be overcome by choosing novel formulation strategies. With this respect, nanotechnology offers a wide range of unexplored possibilities. The unique properties of biodegradable, nanostructured materials, including large surface areas, smart size ranges that enables transport across physiological barriers, ease of engineering and functionalization, possibility for targeting to different organs as well as high loading capacity of actives and various approaches to control the release kinetics, have led to a significant increase in the interest of using nanoparticles in various drug delivery applications.