Novel therapeutic strategy in the treatment of infectious diseases by anti-microbial, endotoxin-neutralizing proteins.

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We have found 18kDa cationic anti-microbial proteins (CAP18) with LPS-neutralizing activity from rabbit and human neutrophils. The 27mer C-terminal fragment of human CAP 18 (27mer ; CAP18_<109-135>) has been identified as the anti-microbial and LPS-neutralizing domain. We investigated the effects of modification and/or substitution of amino acid residues of CAP18 peptides on their activities. Acetylation of N-terminal and amidation of C-terminal residues of the 27mer in-creased LPS-neutralizing and antimicrobial activities. Substitution of E_<119> and K_<128> of 27mer to L (27LL) or F (27FF) increased LPS binding activity (〜30-40 fold) and also blocked LPS-induced lethality in mice. Substitution of E_<119> to L_<119> increased LPS-binding activity (〜8 -fold), however, this peptide (27L) could not protect vs. endotoxin shock. Truncation of 9 amino acids from the N-terminus of 27mer (18mer : CAP18_<118-135>) resulted in a significant decrease in LPS-binding activity even though both terminuses are chemically modified. Increasing the hydrophobic amino acid residues (Leucin=L) in 18mer (18LL) increased LPS-binding activity (〜30-fold) and anti-microbial activity versus gram-positive bacteria such as MRSA (methicillin resistant staphylococcus aureus ; >3 -folds), however, 18LL could not protect vs. endotoxin shock in mice. Further replacement of three positions of 18LL by lysine (K) significantly increased LPS-binding activity (〜120-fold), antimicrobial activity vs. gram negative bacteria such as E.coli O157 : H7 and S.typhimurium, and protect mice from endotoxin shock.From these results, the importance of the stability of alpha-helical structure, and the balance of hydrophobic/ hydrophilic (basic) amino acid residues in CAP18 peptide was suggested.