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

Abstract

BackgroundInhalation 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.MethodsTwo 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.ResultsThe 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.ConclusionThe 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 registrationClinicaltrials.gov: NCT01400568

Reproducibility of the inflammatory response to inhaled endotoxin in healthy volunteers

“…We confirm previous reports of reproducible sputum neutrophilia (1) post-endotoxin challenge and also demonstrate for the first time significant reproducibility for the pro-inflammatory cytokines IL-8, IL-6 and IL-1β in inhaled LPS challenge. Among all our markers of inflammation (including PMN/mg), IL-8 demonstrated the strongest reproducibility.…”

“…Inhaled endotoxin (LPS, lipopolysaccharide) challenge induces increases in sputum neutrophils (PMNs), interleukin (IL)-1β, IL-6 and IL-8, and as such, has been used as a proof of concept model to test the efficacy of anti-inflammatory treatments in airway disease (1-3). Individual reproducibility of the inflammatory response is a necessary component to further validate the applicability of this model.…”

“…Individual reproducibility of the inflammatory response is a necessary component to further validate the applicability of this model. Janssen et al reported that the cumulative sputum PMN response was reproducible within healthy individuals when assessed across three LPS challenges separated by four weeks (1). However, there is notable variability in sputum PMNs following inhaled LPS challenge but potentially less with the cytokine response.…”

Effect of Inhaled Endotoxin on Mucociliary Clearance and Airway Inflammation in Mild Smokers and Nonsmokers

“…(38) More recent studies with LPS challenge have shown a similar time course for LPS-induced inflammation. (39,40) As discussed above, the acute response (immediately post LPS challenge) of MCC in either study group may have been quite different from what we observed at 4 hr. Nevertheless, in this initial study on the effects of LPS exposure on MCC, we wanted to maintain similar timing to our previous studies so that we could compare the MCC and inflammatory responses at or near the same time post challenge.…”

Allergen-Induced Asthmatic Responses Modified by a GATA3-Specific DNAzyme

“…Assessment of cell distribution and analysis of mediators in the supernatant were performed at a central laboratory. 24 Cytokines and chemokines were measured with a type 1 helper T-cell (Th1) and Th2 assay and a chemokine multiplex assay. The tryptase level in sputum supernatants was measured with the use of an enzyme-linked immunosorbent assay.…”