Project Summary
This project explores the development of bicontinuous microemulsions (B¿Es) as topical drug delivery systems
for antimicrobial peptides (AMPs), as an alternative therapy to treat wound infections. This study addresses the
missions of both the NIH’s NIBIB and NIAID research programs through: 1) the development of a novel drug
delivery technology, and 2) a new approach to combat chronic wound infections exacerbated by
antibiotic-resistant microorganisms. Wound infections are a major problem due to the increased occurrence of
antibiotic-resistant microorganisms, which are attributable to $20 billion annually in excess health care costs,
$35 billion in societal costs, and 8 million days of extended hospitalization stays in the US. AMPs can kill
microbial pathogens that cause wound infections (e.g., methicillin-resistant Staphylococcus aureus [MRSA])
through disruption of negatively charged biomembranes, producing pores that allow leakage of cytoplasmic
fluids; however, AMPs must be delivered in a highly folded form to be effective and previous studies have not
addressed this need. Thus, this study proposes to develop B¿Es as systems for encapsulation of AMPs in their
folded state and delivery to wound surfaces. B¿Es are optically clear, homogeneous, and thermodynamically
stable biomembrane mimetic systems. They possess unique drug-delivery properties compared to other
membrane-based systems, including large-volume fractions of water and oil (~40%) that allow co-solubilization
of other drugs. Preliminary studies demonstrate that the AMP melittin when encapsulated into B¿Es can reside
in a highly folded state (>90% ¿-helix) and high concentrations (1-10 g/L) are achievable. Several important
hypotheses will be tested, including that AMP-loaded B¿E solutions are effective antimicrobial agents with
activity strongly controlled by the extent of AMP folding. The Specific Aims are to 1) demonstrate that four
diverse AMPs can be incorporated into several different biocompatible B¿E systems at high (biologically
relevant) concentrations and degrees of folding; 2) show that B¿Es loaded with AMPs and antiseptic agents
such as chlorhexidine (derived in Aim 1) can serve as robust topical preparations for treatment of wound
infections. For Aim 1, the relationship between AMP folding and B¿E properties will be determined through
novel methods, including circular dichroism and small-angle neutron scattering. Aim 2 will provide
measurements of minimum inhibitory and bactericidal concentration against several representative
microorganisms encountered in wounds (including MRSA), cell cytotoxicity (hemolysis) activity and protection
of B¿E-encapsulated AMPs from proteolysis. The results will provide a basis for future clinical applications to
use B¿Es as a drug delivery system for improved activity and/or stability of cell-penetrating peptides. Other
applications include adsorption to surfaces of medical devices for antimicrobial coatings and delivery of
radiolabeled AMPs for bioimaging.