Neutralization of endotoxin in vitro and in vivo by Bac7(1-35), a proline-rich antibacterial peptide

Lipopolysaccharides (LPS), or endotoxins, are structural components of gram-negative bacteria implicated in the pathogenesis of septic shock. In this study the antiendotoxin activity of Bac7(1-35), a synthetic peptide based on the sequence of a proline-rich antibacterial peptide from bovine neutrophils, was investigated in vitro and in an experimental rat model of gram-negative septic shock. The ability of Bac7(1-35) to bind LPS from Escherichia coli O111:B4 was determined using a sensitive Limulus chromogenic assay. In the in vivo study, adult male Wistar rats were given an intraperitoneal injection of 1 x 10(9) colony-forming units of E. coli ATCC 25922. All animals were randomized to receive intraperitoneally 1 mg/kg Bac7(1-35), or isotonic sodium chloride solution (control group C1), 60 mg/kg of piperacillin and 1 mg/kg polymyxin B, 1 mg/kg of polymyxin B plus 60 mg/kg of piperacillin, and 1 mg/kg of Bac7(1-35) plus 60 mg/kg of piperacillin. Each group included 15 animals. Bac7(1-35) was found to completely inhibit the LPS procoagulant activity at approximately 10 microM peptide concentration, as determined by in vitro LAL chromogenic assay. Treatment with Bac7(1-35) resulted in significant decrease in plasma endotoxin levels and lethality rates compared with saline injected control animals. No statistically significant differences were noted between Bac7(1-35) and polymyxin B in reducing all variables measured. These results provide evidence for the ability of Bac7(1-35) to effectively bind LPS and protect animals from lethal effects of this molecule, and point to its potential use for the treatment of endotoxin-induced septic shock.