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Antimicrobial Agents and Chemotherapy, August 2005, p. 3208-3216, Vol. 49, No. 8
0066-4804/05/$08.00+0     doi:10.1128/AAC.49.8.3208-3216.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Activity of the De Novo Engineered Antimicrobial Peptide WLBU2 against Pseudomonas aeruginosa in Human Serum and Whole Blood: Implications for Systemic Applications

Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine,¹ Department of Pediatrics, Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania 15261²

Received 17 December 2004/ Returned for modification 22 February 2005/ Accepted 2 May 2005

Cationic amphipathic peptides have been extensively investigated as a potential source of new antimicrobials that can complement current antibiotic regimens in the face of emerging drug-resistant bacteria. However, the suppression of antimicrobial activity under certain biologically relevant conditions (e.g., serum and physiological salt concentrations) has hampered efforts to develop safe and effective antimicrobial peptides for clinical use. We have analyzed the activity and selectivity of the human peptide LL37 and the de novo engineered antimicrobial peptide WLBU2 in several biologically relevant conditions. The host-derived synthetic peptide LL37 displayed high activity against Pseudomonas aeruginosa but demonstrated staphylococcus-specific sensitivity to NaCl concentrations varying from 50 to 300 mM. Moreover, LL37 potency was variably suppressed in the presence of 1 to 6 mM Mg²⁺ and Ca²⁺ ions. In contrast, WLBU2 maintained its activity in NaCl and physiologic serum concentrations of Mg²⁺ and Ca²⁺. WLBU2 is able to kill P. aeruginosa (10⁶ CFU/ml) in human serum, with a minimum bactericidal concentration of <9 µM. Conversely, LL37 is inactive in the presence of human serum. Bacterial killing kinetic assays in serum revealed that WLBU2 achieved complete bacterial killing in 20 min. Consistent with these results was the ability of WLBU2 (15 to 20 µM) to eradicate bacteria from ex vivo samples of whole blood. The selectivity of WLBU2 was further demonstrated by its ability to specifically eliminate P. aeruginosa in coculture with human monocytes or skin fibroblasts without detectable adverse effects to the host cells. Finally, WLBU2 displayed potent efficacy against P. aeruginosa in an intraperitoneal infection model using female Swiss Webster mice. These results establish a potential application of WLBU2 in the treatment of bacterial sepsis.