Low-dose endotoxin inhalation in healthy volunteers--a challenge model for early clinical drug development

BMC Pulm Med. 2013 Mar 28;13:19. doi: 10.1186/1471-2466-13-19.


Background: Inhalation of endotoxin (LPS) induces a predominantly neutrophilic airway inflammation and has been used as model to test the anti-inflammatory activity of novel drugs. In the past, a dose exceeding 15-50 μg was generally needed to induce a sufficient inflammatory response. For human studies, regulatory authorities in some countries now request the use of GMP-grade LPS, which is of limited availability. It was therefore the aim of this study to test the effect and reproducibility of a low-dose LPS challenge (20,000 E.U.; 2 μg) using a flow- and volume-controlled inhalation technique to increase LPS deposition.

Methods: Two to four weeks after a baseline sputum induction, 12 non-smoking healthy volunteers inhaled LPS on three occasions, separated by at least 4 weeks. To modulate the inflammatory effect of LPS, a 5-day PDE4 inhibitor (Roflumilast) treatment preceded the last challenge. Six hours after each LPS inhalation, sputum induction was performed.

Results: The low-dose LPS inhalation was well tolerated and increased the mean percentage of sputum neutrophils from 25% to 72%. After the second LPS challenge, 62% neutrophils and an increased percentage of monocytes were observed. The LPS induced influx of neutrophils and the cumulative inflammatory response compared with baseline were reproducible. Treatment with Roflumilast for 5 days did not have a significant effect on sputum composition.

Conclusion: The controlled inhalation of 2 μg GMP-grade LPS is sufficient to induce a significant neutrophilic airway inflammation in healthy volunteers. Repeated low-dose LPS challenges potentially result in a small shift of the neutrophil/monocyte ratio; however, the cumulative response is reproducible, enabling the use of this model for "proof-of-concept" studies for anti-inflammatory compounds during early drug development.

Trial registration: ClinicalTrials.gov NCT01400568.

Publication types

  • Clinical Trial

MeSH terms

  • Administration, Inhalation
  • Adolescent
  • Adult
  • Aminopyridines / administration & dosage*
  • Benzamides / administration & dosage*
  • Cyclopropanes / administration & dosage
  • Dose-Response Relationship, Drug
  • Drug Design
  • Endotoxins / administration & dosage*
  • Endotoxins / adverse effects*
  • Endotoxins / immunology
  • Female
  • Healthy Volunteers
  • Humans
  • Lipopolysaccharides / administration & dosage
  • Lipopolysaccharides / adverse effects
  • Lipopolysaccharides / immunology
  • Male
  • Middle Aged
  • Monocytes / immunology
  • Neutrophils / immunology
  • Phosphodiesterase 4 Inhibitors / administration & dosage
  • Pneumonia / chemically induced*
  • Pneumonia / drug therapy*
  • Pneumonia / immunology
  • Reproducibility of Results
  • Research Design
  • Sputum / immunology
  • Young Adult


  • Aminopyridines
  • Benzamides
  • Cyclopropanes
  • Endotoxins
  • Lipopolysaccharides
  • Phosphodiesterase 4 Inhibitors
  • Roflumilast

Associated data

  • ClinicalTrials.gov/NCT01400568