Influence of Synthetic Antiendotoxin Peptides on Lipopolysaccharide (LPS) Recognition and LPS-Induced Proinflammatory Cytokine Responses by Cells Expressing Membrane-Bound CD14

Abstract

Lipopolysaccharides (LPS), or endotoxins, are major structural and functional components of the outer membrane of gram-negative bacteria (24). These complex macromolecules exhibit a variety of toxic and proinflammatory activities that are associated with the lipid A moiety and are causally related to the pathogenesis of gram-negative sepsis and septic shock (17, 18).Many of the local and systemic pathophysiologic phenomena produced by LPS in the exposed host result from the ability of LPS to activate host inflammatory cells (7), including monocytes, macrophages, and polymorphonuclear leukocytes. Recent attention has focused on putative LPS receptors found on the surfaces of these cells, the relation of these receptors to LPS-induced signal transduction, and the role of each in the development of proinflammatory responses.Membrane-bound CD14 (mCD14), a glycosyl phosphatidylinositol-anchored protein expressed on myeloid cells, is the best characterized LPS receptor identified to date (9, 33, 37). mCD14 appears to be part of a multicomponent LPS receptor functionally linked to the initiation of intracellular signaling events related to LPS-induced cell activation (29). The signaling unit of the LPS receptor is comprised of members of the Toll-like receptor family of transmembrane proteins characterized by their amphiphilic properties and leucine-rich repeats (31, 36). Serum-associated LPS-binding protein (LBP), which forms complexes with LPS through high-affinity attachment to the lipid A moiety, catalyzes LPS recognition by mCD14, resulting in the generation of LPS-induced proinflammatory signals (12,14).Recent experiments have attempted to define the roles of mCD14 and LBP in LPS-related septic events as well as the possible protective or therapeutic activities of proteins, including antibodies, that neutralize LPS by interrupting its proinflammatory interactions with mCD14 and LBP.We previously showed that LPS-specific monoclonal antibodies (MAbs) are capable of neutralizing cytokine-and transcription factor-inducing activities of LPS by inhibiting the binding of LPS to mCD14 expressed on human peripheral blood monocytes (PBMC) and on CD14-transfected Chinese hamster ovary fibroblasts (CHO-CD14 cells) (20,21).Polymyxin B (PMB), a cationic, cyclic peptide antibiotic, inhibits biological activities of LPS through high-affinity bind-* Corresponding author. Mailing address:

Augmentation of the Lipopolysaccharide-Neutralizing Activities of Human Cathelicidin CAP18/LL-37-Derived Antimicrobial Peptides by Replacement with Hydrophobic and Cationic Amino Acid Residues

“…In this study, to develop cathelicidin-derived antimicrobial peptides with improved LPS-neutralizing activities, we utilized the 18-mer peptide (K 15 -V 32 ) of human cathelicidin hCAP18/ LL-37 as a template and evaluated the activities of its peptide derivatives. By replacement of E 16 and K 25 with two L residues, the hydrophobicity of the peptide was increased and the hydrophobic sector in the helix was extended ( Fig. 1 and 11; compare 18-mer K 15 -V 32 with 18-mer LL).…”

“…For prevention of bacterial infections and their related symptoms (e.g., gram-negative bacterial septic shock), much attention has been focused on the low-molecular-weight cationic antimicrobial peptides that possess both antibacterial and LPS-neutralizing activities (5,14,16,17,20,28,33,40,49). Previously, it was demonstrated that in addition to exhibiting potent antibacterial activity against gram-positive and gramnegative bacteria (34), hCAP18/LL-37 could bind to the lipid-A moiety of LPS and inhibit the interaction of LPS with LBP, which transports LPS to CD14 ϩ cells, thereby suppressing the binding of LPS to CD14 ϩ cells (33) and possibly attenuating Toll-like receptor-mediated CD14 ϩ cell activation (2,4,19,48).…”

Cathelicidin Family of Antibacterial Peptides CAP18 and CAP11 Inhibit the Expression of TNF-α by Blocking the Binding of LPS to CD14+ Cells

“…Furthermore, Iwagaki et al (40) investigated the binding of LPS to CD14 ϩ cells using synthetic antiendotoxin peptides that were designed to mimic the structures of polymyxin B, which inhibits the biological activities of LPS through its high affinity binding to the lipid A moiety of LPS. In addition, Dankesreiter et al (41) synthesized the hybrid peptides containing LPS-binding domains from Limulus anti-LPS factor and LBP and examined their effects on the interaction of LPS with CD14 ϩ cells.…”

Receptors, Mediators, and Mechanisms Involved in Bacterial Sepsis and Septic Shock

“…Peptides based on BPI (172), LBP (78), CAP18 (264), CAP37 (50), lactoferrin (615), SAP (87), Limulus anti-LPS factor (LAL) (451), bee melittin (479,480), silk moth cecropin (479,480), and the antibiotic peptide polymyxin B (238) have been constructed and tested on bactericidal, LPS-or LTA-binding, and neutralizing potency in vitro and in vivo. The results with these peptides with respect to binding, neutralization, and bactericidal activity are promising, but it was shown that the spatial organization of the positive and hydrophobic moieties largely determines the binding affinity of the peptides for the bacterial compounds (238,354). Further investigations are needed to determine an optimal structure and may lead to the construction of a potent and highly specific peptide-based antibiotic and LPS-and LTA-neutralizing peptide.…”