Encapsulation of Melittin in Bicontinuous Microemulsions for Topical Delivery

Abstract

Surgical site infections and chronic wounds, especially those caused by antibiotic-resistant microorganisms, result in hospitalization and fatalities each year. Methods to prevent these infections, such as cleaning and preparing medical tools, have had minimal success in preventing infections. Further, antibiotic treatments have become less successful in treating infections and wounds as a result of antibiotic-resistant bacteria. Antimicrobial peptides (AMP) are a possible treatment solution. AMPs are oligopeptides that occur in nature or can be synthesized in vitro which possess a broad spectrum of antimicrobial activity against bacteria and other harmful microorganisms. AMPs operate by disrupting the packing arrangements of biomembranes in prokaryotes through their insertion into negatively charged phospholipid bilayers. However, many AMP products have failed clinical trials because of their difficulty to be delivered at high concentrations in an active form. This project proposes the use of bicontinuous microemulsions (BMEs) to encapsulate and deliver AMPs. BMEs are thermodynamically stable monophasic solutions consisting of surfactant, oil, aqueous media, and sometimes a cosurfactant. They are optically clear and consist of surfactant monolayers that separate oil and water nanodomains. Several different BME systems composed of biocompatible oils such as isopropyl myristate and limonene were evaluated for their ability to encapsulate melittin, a model AMP, and to test the system’s antimicrobial activity. AMPs are typically cationic, and the following hypothesis is being tested, that BMEs created with anionic surfactants would induce a more highly folded, hence more biologically active, conformation for melittin. We are currently measuring the antimicrobial activity of BME-encapsulated melittin against several prominent bacteria that are present in chronic wounds and surgical site infections through multiple antimicrobial assays. We will also assess the structure and microenvironment of melittin using circular dichroism and fluorescence spectroscopy, respectively, and the impact of melittin on the structure of BMEs through small-angle X-ray scattering.