May 2008
Volume 49, Issue 13
ARVO Annual Meeting Abstract  |   May 2008
Influence of Local Concentration on the Antimicrobial Efficacy of the Cathelicidin LL-37
Author Affiliations & Notes
  • G. Qin
    University of Houston, Houston, Texas
  • C. Cai
    University of Houston, Houston, Texas
  • A. McDermott
    University of Houston, Houston, Texas
  • Footnotes
    Commercial Relationships  G. Qin, None; C. Cai, None; A. McDermott, None.
  • Footnotes
    Support  NSF early Faculty CAREER Award, NIH EY13175, NIH EY007551
Investigative Ophthalmology & Visual Science May 2008, Vol.49, 4790. doi:
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      G. Qin, C. Cai, A. McDermott; Influence of Local Concentration on the Antimicrobial Efficacy of the Cathelicidin LL-37. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4790. doi:

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose: : LL-37 is an antimicrobial peptide expressed by ocular surface epithelial cells that has antibacterial activity and can modulate immune responses and wound healing and so has potential clinical uses. Evidence suggests that a high local concentration of antimicrobial peptides present in vivo facilitates the disruption of bacterial membranes. Here we investigated the effect of localizing LL-37 to surfaces on its antibacterial activity.

Methods: : LL-37 was immobilized onto oligo (ethylene glycol) monolayers presenting carboxylic acid groups on gold substrates through electrostatic interactions. The coated surfaces were characterized by X-ray photoelectron spectroscopy and ellipsometry. The antibacterial effect of immobilized LL-37 was measured against a P. aeruginosa strain expressing green fluorescent protein (PA01-GFP). The coated surfaces were incubated with 100ul of a 4x108 cfu/ml bacterial suspension for up to 2 h. Propidium iodide was used to stain bacteria with compromised cell membranes. Fluorescence images were captured digitally and the number of bacteria was counted using ImagePro software.

Results: : Analysis showed that the surface concentration of LL-37 was on the order of 1013 molecules/cm2, equivalent to a concentration in the ng/mL range were the peptide to be dissolved in solution under the current conditions. Previous studies showed that effective killing by LL-37 in solution required concentrations in the ug/ml range. At a surface concentration of 4.4x1013 molecules/cm2 LL-37 showed significant antimicrobial efficacy with ~ 97% of PA01-GFP adsorbed on the surfaces having compromised membranes (n=3). Notably, we observed a sharp increase in bacterial killing when the surface density of LL-37 exceeded 3.3x1013 molecules/cm2, suggesting cooperative effects. Furthermore, a kinetic study showed that the adsorption and killing of bacterial cells occurred within 3 min.

Conclusions: : Our findings suggest that localization of LL-37 on surfaces greatly increased its antimicrobial efficacy, that molecules of LL-37 act cooperatively and that the adsorption and killing of bacterial cells were rather rapid. These results indicate that LL-37 may have significant activity in vivo when presented in an appropriate manner thus may be useful clinically to prevent and treat ocular surface infection.

Keywords: pseudomonas • keratitis • cornea: basic science 

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