Poly-L-Lysine compacts DNA, kills bacteria, and improves protease inhibition in cystic fibrosis sputum

Am J Respir Crit Care Med. 2013 Sep 15;188(6):703-9. doi: 10.1164/rccm.201305-0912OC.


Rationale: Neutrophil serine proteases in cystic fibrosis (CF) lung secretions partially resist inhibition by natural and exogenous inhibitors, mostly because DNA impairs their control. Cationic polypeptides display the property of condensing DNA and retain antimicrobial properties. We hypothesized that DNA condensation by cationic polypeptides in CF sputum would result in a better control of CF inflammation and infection.

Objectives: We examined whether poly-L-lysine would compact DNA in CF lung secretions and liquefy CF sputum, improve the control of extracellular proteases by exogenous inhibitors, and whether it displays antibacterial properties toward CF-associated bacteria.

Methods: We used fluorogenic methods to measure proteolytic activities and inhibition by protease inhibitors in whole sputum homogenates from patients with CF before and after treatment with poly-L-lysine. Antibacterial properties of poly-L-lysine were measured in bacterial cultures and in whole CF sputum. Poly-L-lysine toxicity was evaluated after aerosolization by histologic analysis, flow cytometry, and quantification of proinflammatory cytokines.

Measurements and main results: Poly-L-lysine compacts CF sputum DNA, generating a liquid phase that improves ciliary beating frequency at the lung epithelial surface, and allows the control of neutrophil elastase and cathepsin G by their natural inhibitors. It retains antimicrobial properties against Pseudomonas aeruginosa and Staphylococcus aureus at doses that induce no inflammation in the mouse lung after aerosol administration.

Conclusions: Poly-L-lysine may be an alternative to dornase-α to liquefy sputum with added benefits because it helps natural inhibitors to better control the deleterious effects of extracellularly released neutrophil serine proteases and has the ability to kill bacteria in CF sputum.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Animals
  • Anti-Bacterial Agents / pharmacology*
  • Cathepsin G / drug effects
  • Cathepsin G / metabolism
  • Cystic Fibrosis / drug therapy*
  • Cystic Fibrosis / metabolism
  • DNA / drug effects*
  • DNA / metabolism
  • Disease Models, Animal
  • Female
  • Flow Cytometry / methods
  • Humans
  • Leukocyte Elastase / drug effects
  • Leukocyte Elastase / metabolism
  • Lung / drug effects
  • Lung / metabolism
  • Lysine / pharmacology*
  • Male
  • Mice
  • Middle Aged
  • Neutrophils / drug effects
  • Neutrophils / metabolism
  • Peptide Hydrolases / drug effects*
  • Peptide Hydrolases / metabolism
  • Proteolysis / drug effects
  • Pseudomonas aeruginosa / drug effects
  • Sputum / drug effects*
  • Sputum / metabolism
  • Staphylococcus aureus / drug effects


  • Anti-Bacterial Agents
  • DNA
  • Peptide Hydrolases
  • Cathepsin G
  • Leukocyte Elastase
  • Lysine