A synthetic peptide derived from bactericidal/permeability-increasing protein neutralizes endotoxin in vitro and in vivo.

Lipopolysaccharide (LPS [endotoxin]), a structural component of gram-negative bacteria, is implicated in the pathogenesis of septic shock. Lipid A is an evolutionarily conserved region of LPS that has been identified as the toxic component of LPS. Therapeutic strategies for the treatment of septic shock in humans are currently focused on neutralization of LPS. Here, the anti-endotoxin activity of BNEP, a synthetic peptide derived from the human bactericidal/permeability-increasing protein (BPI; aa 148-161) was investigated in vitro and in experimental animal endotoxemia models in vivo. The ability of BNEP to bind LPS from Escherichia coli O55:B5 and lipid A from Salmonella Re 595 was tested using an affinity sensor assay, and its ability to neutralize LPS was tested using a sensitive Limulus amebocyte lysate (LAL) assay. Polymyxin B (PMB) was used as the positive control in the in vitro experiments and in mouse experiments. We found that BNEP and PMB bound LPS with a similar affinity (Kd values of 25.4 and 25.8 nM, respectively). In contrast, BNEP bound lipid A with a slightly lower affinity than that of PMB (Kd values of 8 and 5.6 nM, respectively). The exact capacity of BNEP binding to LPS was approximately 0.53 microg peptide per 1 ng of LPS, as shown by affinity sensor assay. The LAL test showed that 256 microg of BNEP almost completely neutralized 2 ng LPS. In vivo, mice were randomized, intravenously injected with BNEP (0.5-10 mg/kg) or 1 mg/kg PMB, and then lethally challenged with 20 mg/kg LPS. We found that 5 mg/kg BNEP significantly protected mice from LPS challenge. In an endotoxemia rat model, animals were co-treated with 5 or 10 mg/kg BNEP and 10 mg/kg LPS via cardiac catheter. BNEP treatment resulted in significant reduction of tumor necrosis factor alpha (TNF-alpha) and IL-6, compared with LPS-only control animals. In addition, 10 mg/kg BNEP-treated animals showed a significant decrease in plasma endotoxin levels in comparison to animals treated with LPS alone. These results provide evidence that BNEP effectively neutralizes LPS in vitro and in vivo, and could protect animals from the lethal effects of LPS via decreasing plasma endotoxin and proinflammatory cytokines. Our work suggests that this peptide is worthy of further investigation as a possible novel treatment for septic shock.