Evaluation of the ability of LL-37 to neutralise LPS in vitro and ex vivo.
BACKGROUND
Human cathelicidin LL-37 is a cationic antimicrobial peptide (AMP) which possesses a variety of activities including the ability to neutralise endotoxin. In this study, we investigated the role of LPS neutralisation in mediating LL-37's ability to inhibit Pseudomonas aeruginosa LPS signalling in human monocytic cells.


RESULTS
Pre-treatment of monocytes with LL-37 significantly inhibited LPS-induced IL-8 production and the signalling pathway of associated transcription factors such as NF-κB. However, upon removal of LL-37 from the media prior to LPS stimulation, these inhibitory effects were abolished. These findings suggest that the ability of LL-37 to inhibit LPS signalling is largely dependent on extracellular LPS neutralisation. In addition, LL-37 potently inhibited cytokine production induced by LPS extracted from P. aeruginosa isolated from the lungs of cystic fibrosis (CF) patients. In the CF lung, polyanionic molecules such as glycosaminoglycans (GAGs) and DNA bind LL-37 and impact negatively on its antibacterial activity. In order to determine whether such interactions interfere with the LPS neutralising ability of LL-37, the status of LL-37 and its ability to bind LPS in CF sputum were investigated. Overall our findings suggest that in the CF lung, the ability of LL-37 to bind LPS and inhibit LPS-induced IL-8 production is attenuated as a result of binding to DNA and GAGs. However, LL-37 levels and its concomitant LPS-binding activity can be increased with a combination of DNase and GAG lyase (heparinase II) treatment.


CONCLUSIONS
Overall, these findings suggest that a deficiency in available LL-37 in the CF lung may contribute to greater LPS-induced inflammation during CF lung disease.
Centre for Infection and Immunity, School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast, Belfast, Northern Ireland.
Aaron
A
Scott
Sinéad
S
Weldon
Paul J
PJ
Buchanan
Bettina
B
Schock
Robert K
RK
Ernst
Danny F
DF
McAuley
Michael M
MM
Tunney
Chris R
CR
Irwin
J Stuart
JS
Elborn
Clifford C
CC
Taggart
D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D023181:Antimicrobial Cationic Peptides / Q000494:pharmacology*; D000992:Antitoxins / Q000494:pharmacology*; D045744:Cell Line, Tumor; D003550:Cystic Fibrosis / Q000382:microbiology; D004247:DNA / Q000378:metabolism; D006025:Glycosaminoglycans / Q000378:metabolism; D006801:Humans; D016209:Interleukin-8 / Q000096:biosynthesis; D008070:Lipopolysaccharides / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D008168:Lung / Q000382:microbiology; D009000:Monocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D011550:Pseudomonas aeruginosa / Q000737:chemistry; D015398:Signal Transduction / Q000187:drug effects; D054804:Cathelicidins
D000893:Anti-Inflammatory Agents; D023181:Antimicrobial Cationic Peptides; D000992:Antitoxins; D006025:Glycosaminoglycans; D016209:Interleukin-8; D008070:Lipopolysaccharides; D004247:DNA; D054804:Cathelicidins