Background. Bactericidal permeability increasing protein (BPI), Limulus anti-lipopolysaccharide factor (LALF), and lipopolysaccharide binding protein (LBP) are three distinct proteins that bind to lipopolysaccharide (LPS). Intriguingly, binding of BPI and LALF to LPS results in neutralization of LPS activity, whereas the binding of LBP to LPS creates a complex that results in augmentation of LPS activity. Despite their different effector functions, we hypothesized that peptides based on the sequences of the proposed LPS-binding motif from each protein would neutralize LPS in vitro. Methods. Three peptide sequences, each 27 amino acids in length, of the proposed LPS-binding motif of BPI (BG38), LALF (BG42), and LBP (BG43) were synthesized. These peptides were then tested for their: (1) ability to inhibit macrophage secretion of TNF-α after stimulation by LPS derived from Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Serratia marcescens; and (2) bactericidal activity against these same four gram-negative bacteria in vitro. Results. Synthetic peptides BG38 (BPI-derived), BG42 (LALF-derived), and BG43 (LBP-derived) but not control peptide significantly inhibited LPS-induced tumor necrosis factor-α secretion by macrophages and mediated the lysis of gram-negative bacteria in vitro. In addition, preincubation of LPS with peptide BG38 mediated complete protection subsequent to lethal endotoxin challenge. Conclusions. These data demonstrate that small peptides derived from BPI, LALF, and LBP retained significant endotoxin-netralizing and bactericidal activity against many different gram-negative bacteria in vitro. Identification of this conserved LPS-binding region within each protein may aid in the development of new immunomodulatory reagents for use as adjuvant therapy in the treatment of gram-negative bacterial sepsis.
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GRAM-NEGATIVEB ACTERIALS EPSISa nd shock remain a significant source of morbidity and death in hospitalized patients. Despite improvements in antimicrobial therapy and intensive care (e.g., aggressive fluid resuscitation, hemodynamic monitoring, and metabolic support), the overall mortality attributable to this disease process remains approximately 40% even in recent large clinical studies. I, 2 Lipopolysaccharide (LPS, endotoxin) is an integral component of the gram-negative Supported by grant ROt GM32414 from the National Institutes of Health. Presented at the Fifty-sixthA nnual Meeting of the Societyo f University Surgeons, Denver, Colo., Feb. 9-11, 1995. Reprint requests: David L. Dunn, MD, PhD, Box 242 Mayo Building, 420 Delaware Street, S.E., Minneapolis, MN 55455. Copyright 9 1995 by Mosby-YearB ook, Inc. 0039-6060/95/$3.00 + 0 11/6/64960 bacterial cell membrane and is responsible for many, if not all, of the toxic effects that occur during gram-negative bacterial sepsis. LPS directly stimulates host macrophages to secrete a wide array of cytokines that include tumor necrosis factor--a (TNF-a), interleukin-1, and interleukin-6. Excessive release of these cytokines by host macrophages almost assuredly contributes to the organ failure and death that occur subsequent to episodes of gram-negative bacterial sepsis. 3 Bactericidal permeability increasing protein (BPI), Limulus anti-LPS factor (LALF), and lipopolysaccharide binding protein (LBP) are three endogenous proteins that bind to LPS. BPI is a 55 kd protein produced within polymorphonuclear leukocyte azurophilic granules and acts specifically against gram-negative bacteria to cause (1) bacterial killing and lysis and (2) endotoxin neutralization. 4-s In addition, pretreatment of animals with BPI reduces the mortality of a subsequent challenge