Bacterial endotoxins (lipopolysaccharide, LPS) from the outer leaflet of the outer membrane of Gram-negative bacteria are among the most effective natural compounds in triggering the human innate immune system. This may be beneficial at low but pathophysiological at high LPS concentrations, the latter leading to the severe septic shock syndrome with still high mortality rates especially in intensity care units.
One approach to inactivate compounds such as LPS is the use of cationic amphiphilic peptides based on natural endotoxin- binding proteins, which are designed to neutralize bacterial LPS and thus inhibit its interaction with relevant mammalian binding proteins/ receptors such as lipopolysaccharide-binding protein (LBP), CD14, and TLR4/MD2. We have designed and synthesized peptides based on human lactoferricin, and have applied in an iterative process (first to third generation) various experimental systems to test their ability to fight against bacterial sepsis. Here, four compounds from the third generation were selected, with and without a short hydrocarbon chain, and analysed in detail starting from biophysical over cell biological and microbiological assays up to animal experiments. Thus, we were able to characterize the parameters relevant in endotoxin deactivation, as part of the bacterial cell as well as in isolated form. The most important parameters include the peptide length, number of cationic amino acids, and hydrophobicity of the peptides.