Salivary mucins inhibit antibacterial activity of the cathelicidin-derived LL-37 peptide but not the cationic steroid CSA-13.
OBJECTIVE
Cationic antimicrobial peptides (CAPs) are the effector molecules of innate immunity, similar in potency to classic antibiotics that function in the first-line of defence against infectious agents. The purpose of this study was to investigate the effects of negatively charged mucins on the antibacterial activity of the positively charged cathelicidin LL-37 peptide, its synthetic analogue WLBU2 and the antimicrobial cationic steroid CSA-13.


METHODS
Mucin, DNA, F-actin and hCAP-18/LL-37 in saliva samples were evaluated by microscopy or immunoblotting. Bacterial killing assays and determination of MICs were used to determine bactericidal activity. Binding of rhodamine-B-labelled LL-37 peptide to mucin was fluorimetrically assessed.


RESULTS
Microscopic evaluation of saliva after addition of rhodamine-B-labelled LL-37 showed localization similar to that observed after the addition of a specific mucin-binding lectin. Immunoblotting confirmed the presence of hCAP-18/LL-37 in saliva samples and LL-37 peptide bound to isolated submaxillary gland mucin-coated plates. Mucin/LL-37 binding was partially prevented by treatment of mucin with neuraminidase, indicating involvement of sialic acid moieties. Decreased LL-37 and WLBU2 antibacterial activity was observed in the presence of mucin or dialysed human saliva, whereas CSA-13 antibacterial activity was significantly resistant to inhibition by mucins.


CONCLUSIONS
This study shows that the antibacterial LL-37 peptide and its synthetic analogue WLBU2 are inhibited by salivary mucin and that the cationic steroid CSA-13 retains most of its function in the presence of an equal amount of mucin or saliva.
Bucki
Robert
R
Department of Physiology, Institute for Medicine and Engineering, University of Pennsylvania, 1010 Vagelos Research Laboratories, 3340 Smith Walk, Philadelphia, PA 19104, USA. buckirob@mail.med.upenn.edu
Namiot
Dorota B
DB
Namiot
Zbigniew
Z
Savage
Paul B
PB
Janmey
Paul A
PA
D000900:Anti-Bacterial Agents / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D023181:Antimicrobial Cationic Peptides / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D015169:Colony Count, Microbial; D006801:Humans; D015151:Immunoblotting; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability; D009077:Mucins / Q000378:metabolism*; D012463:Saliva / Q000737:chemistry* / Q000378:metabolism; D013256:Steroids / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D054804:Cathelicidins
D000900:Anti-Bacterial Agents; D023181:Antimicrobial Cationic Peptides; D009077:Mucins; D013256:Steroids; C521528:ceragenin CSA-13; D054804:Cathelicidins